The Campus Green Guide

The Campus Green House Project by Gooseberry Jam Educlubs


OPENING NEW WORLDS OF GROWING EXPERIENCES

INTRODUCING GREENHOUSE GARDENING INTO THE CLASSROOM ENRICHES THE CURRICULUM


"Through this project-based curriculum, I have seen kids begin to realize that a plant is a living thing and that what they do to that plant on a day-to-day basis matters," shares Sandy May-Fitzgerald, a special education biology teacher.     At a time when our education system is under fire--from parents, politicians, special-interest groups, and national education reformers--some truths about learning endure. Children do enjoy thinking, raising questions, manipulating, sorting, testing, and investigating for themselves.
What can be more engaging than nurturing and exploring living things? National Gardening Association is committed to helping teachers expand their own skills as they help students use plants and gardens as contexts for developing a deeper, richer understanding of the world around them.
This online guide to school greenhouses is not a complete how-to, but rather, a basic overview of key issues relevant to educators planning to run--or currently running--a school greenhouse program. It covers operational and horticultural topics, with an emphasis on how to actively involve students in maintenance and investigations.
You may already use a school greenhouse and want to make it an even more useful learning tool, have one that has fallen into disuse that you'd like to restore, or be contemplating building or purchasing a greenhouse. Greenhouse growing presents a unique set of challenges, and this online guide highlights steps for meeting those challenges.

WHY SCHOOL GREENHOUSES?

CONSIDERING GREENHOUSE GARDENING


"The greenhouse is a resource, much like the library," notes Joyce Harris, greenhouse manager in McLean, VA. "It's also very magical." She continues, "There's nothing like being in a greenhouse in the winter, especially when it's snowing outside."Integrating greenhouse growing into the school year and curriculum takes time and planning.With all of the demands you already face as an educator, why take on a greenhouse project?
When students step into a greenhouse, it is clear that the classroom walls have disappeared, and the opportunities for investigating and learning have begun. With so many senses stimulated, students can't help but become curious observers and active inquirers. A greenhouse is an ecological island separated from its surroundings, experiencing its own seasonal and annual cycles, and featuring fascinating and complex interrelationships. Your students can examine and adjust the climate while exploring plants and other organisms.
Even in a small greenhouse, students learn about plants as whole systems. They can experiment with water movement, pollination, and nutrition, and explore relationships between plants and insects. They can try to simulate different habitats, and understand how physical factors and climate relate to plant type and growth.
Integrating a greenhouse as a learning environment offers boundless opportunities for promoting student responsibility, and helps develop students' confidence and pride as they display and share the fruits (and vegetables and flowers) of their labours.



Selecting a Greenhouse

GREENHOUSE QUESTIONS AND CONSIDERATIONS

If your school is considering building, purchasing, or resurrecting a greenhouse, there are a number of factors to consider--and questions to ask--long before you begin designing planting projects. This section highlights some of those factors.
Your decision about the type of greenhouse will be influenced by how you plan to use it.

PLANNING QUESTIONS

Gather key participants in your school to answer the following questions early in the planning process:
·      What are our goals in initiating a greenhouse program?
·      How do we envision using a greenhouse? (For student plant experiments? For teaching plant science concepts? For extending the outdoor gardening season? For a plant business?)
·      How many students would we like to use the greenhouse at one time? Which grades will be involved?
·      How do we want to integrate it into the curriculum at different grade levels and in different subject areas? During which seasons do we hope to use the greenhouse?
·      Who are resource people in the school experienced at indoor and/or greenhouse gardening? In the community? How much time can they commit to the project?
·      Who will be responsible for the technical aspects of greenhouse operation?
·      How committed are the school district, board, faculty, and staff to the greenhouse project?
·      Might vandalism be a problem? How can we guard against it?
·      Where might we get funding?
Talk with greenhouse builders and people at nurseries, botanical gardens, and other schools that have greenhouses to gather information specific to your situation.

GREEN THUMB HISTORY

The earliest recorded greenhouse was built about 30 A.D. for the Roman emperor Tiberius. Because glass had not been invented, the greenhouse (called a specularium, from the Latin "to look") was made of small clear pieces of mica, a naturally occurring mineral. It was quite time-consuming to build and was devoted to growing delicate citrus fruits. For the next 1,500 years, the wealthy people who did own greenhouses raised exotic fruits and flowers. From the 1800s on, developments in technology provided new materials at lower cost and higher efficiency. What more can your students learn about the history of greenhouses?

Greenhouse Styles

 

Greenhouses can be either freestanding or attached to a building and come in a variety of styles. Most commercial greenhouses are freestanding structures built in exposed areas with plenty of sunlight (maximum sunlight is the most important factor for efficient plant growth).
A freestanding greenhouse could be a permanent structure, complete with a foundation and automated controls, or a simpler (and much less expensive) hoop-type structure that helps you start growing garden plants earlier in the spring and extend the season for  some vegetables into the fall. Freestanding greenhouses do have some drawbacks: In a school setting, they may be less accessible to classrooms and to sources of electricity and water, and heating costs tend to be higher. Attached greenhouses are generally more accessible, cost less to heat, and are closer to water and other services; however, they are typically more costly to construct and receive less total light than freestanding structures. For more greenhouse styles, take a look at our selection in the Gardening with Kids Shop.

Figuring Costs

The cost of building or buying a greenhouse varies tremendously. It could range from several hundred dollars for an unheated polyethylene greenhouse to $3,500 or more for a year-round, automated, heated structure. Northern climate growers should consider the cost of heating, while schools in southern climates need to be more concerned with ventilating and cooling.
The cost of materials for the actual structure--frame, glazing, doors, and vents--is only part of the equation. A greenhouse structure itself, in fact, may account for only 40 percent of the ultimate budget for the entire project.
Other significant expenses to account for include:
·      preparing the site
·      laying the foundation
·      accessories (fans, benches, trays, potting soil, fertilizers, watering equipment, and shading)
·      electricity, heat, and water supply
·      installing automated timers for heat, water, or ventilation, if needed
·      future re-glazing
When shopping for a greenhouse, always ask for written quotations, including shipping costs, for basic materials and accessories. Prepare a budget, and be sure your funding is in place before breaking ground. For more funding ideas, visit the Finding Support and Funds section.

Location

Whether your greenhouse is attached or freestanding, it's important to choose a location (site) that will give you the most sunlight when it's in use, during fall and spring for most schools.
A greenhouse that's attached to a building above 40° north latitude should have an east/west orientation with the glazed area facing south to provide optimum winter sunlight. Greenhouses located below 40° north latitude can have a north/south orientation to take advantage of eastern or western exposures. Whether your greenhouse is attached or freestanding, it's important to choose a location (site) that will give you the most sunlight when it's in use, during fall and spring for most schools.
You should locate a freestanding greenhouse no closer than a distance of two and a half times the height of any wall or other object that might block sunlight. Also assess the role tree shade will play in your proposed site.
You'll also want to consider factors such as access to water, potting and planting areas, and ease of access for students. In any case, the site you choose should be well drained and not subject to settling of water or cold air.

Glazing

The material that covers a greenhouse and through which the sunlight passes is called glazing. There are many types available, each with advantages and disadvantages. These include glass, acrylic, polycarbonate panels, polyethylene films, and fiberglass. If you're building, buying, or reconstructing a greenhouse, you'll want to talk with experts and manufacturers about the pros, cons, and costs of various materials. As you review your options, be aware of these general considerations:
·      Light transmission and energy efficiency--The degree to which glazing allows light energy to enter and prevents the heat from leaving is known as its efficiency. This is affected by thickness, number of layers, and type of material.
·      Life span--Plastic glazing can last from 1 to 20 years, depending on the type and treatment of the materials.
·      Special treatments--Some greenhouse glazing is designed to be especially effective at trapping heat. Some is treated so it is antistatic (attracting less dust and preventing condensation from forming on the inside surface). Some types of glazing diffuse and reflect the incoming light to reduce shadows.
·      Safety--Some types of glazing are flammable; others, like glass, are breakable.
·      Hail resistance--Hail can batter your greenhouse and your hopes, so select a glazing that can withstand an onslaught if severe hail is likely in your region. A rigid type of glazing would be best under these conditions.

Greenhouse Conditions

GREENHOUSE ENVIRONMENTS REQUIRE SOME CONTROL AND MONITORING

While a greenhouse can provide a delightful environment where living things thrive, it is an artificial environment in which you attempt to control as many factors as possible for the benefit of your plant denizens. It helps to recall what actually makes plants grow. Plants convert light into energy (sugar) during photosynthesis. This process requires light, carbon dioxide, temperatures between 45°F and 85°F, and water. None of these factors operates independently; rather, they affect and are affected by one another, as well as by your greenhouse design.
Your control of these variables will be influenced by:
·      the general type of greenhouse you have
·      your local climate
·      the climatic controls you have available in your greenhouse

SETTING UP THE SPACE

Consider a number of factors when setting up the inside of your greenhouse:
·      How many students will be working there at once?
·      Will they work individually or in small groups?
·      What types of projects will you be working on?
·      How can you make it safe, comfortable, and user-friendly?
The layout and height of benches for plants and design of the aisles should allow for handicapped access (doors and aisles a minimum of 4 feet wide.) Some of the benches should be 2 feet high or more, to allow for wheelchair seating. You'll also want to consider the height of the students. Either make bench heights adjustable or include several bench heights.
Invite students to help plan the inside greenhouse setup, personalize some parts of it, or create special areas. A peninsula design for the raised work areas or benches is often well suited for research, experimental projects, and group management. Some schools find that a horseshoe arrangement of planting surfaces provides more room for plants around three sides while leaving room in the center for movement and discussion. Movable planting benches on rollers are efficient and flexible, but can be expensive.
Consider how you will make water accessible and where you'll store soil mixes, fertilizers, and pots. You'll also need a work area for planting and germinating seeds and for taking root cuttings. Consider creating a spot protected from dampness, in or near the greenhouse, to keep plant- and greenhouse-related reference books.

Greenhouse Climates

The following greenhouse characterizations are based on the temperature that can be maintained inside the greenhouse. They range from the least to the most expensive to build and maintain. Refer to this information when reviewing what you want to grow in your greenhouse.

COLD GREENHOUSE

A cold greenhouse, the least expensive to maintain, is a freestanding structure that is heated by the sun only. If you're in a cold-winter area, the inside greenhouse temperature may be only 10 degrees above the outside temperature. This type of greenhouse is typically used to start or house seedlings in late winter or spring (three to four weeks ahead of outside planting time). It can also be used through the summer and into early fall to grow selected plants. In an area with cold winters, it might be used for overwintering semi-hardy outdoor plants, but more commonly would be shut down.

COOL GREENHOUSE

This type of greenhouse can maintain a minimum temperature of 42 to 45° F. In cold-weather areas, such a greenhouse would be heated during winter months. It can be used to overwinter frost-sensitive plants, to start plants three to four weeks ahead of the cold greenhouse, to raise warm-season crops through the summer, and to grow some cool-weather crops into the fall and winter. It might also be used year-round as a conservatory for desert plants.

WARM GREENHOUSE

This type of greenhouse can maintain a minimum temperature of 55° F, with additional heat during the day and night, as needed, depending on its location. It can be used through the year for a range of growing projects, with heating expenses rising as winter temperatures drop. It provides good conditions for growing vegetables and many annuals to maturity and for conducting a wide range of research projects throughout the school year.

HOT GREENHOUSE

This type of greenhouse, the most expensive to maintain, sustains a minimum temperature of 65° F with additional heat throughout the year. While too warm for many vegetable plants, it can be used for raising subtropical and tropical plants.

Light

Light provides the energy necessary for plants to produce food through photosynthesis. Even though the amount of light inside your greenhouse usually depends on the amount of natural sunlight available, it's helpful to understand a bit about plants' light needs.
Plants require certain quantities of light for proper growth. Light is often measured in footcandles. A footcandle equals the amount (intensity) of light produced in a completely dark space by one candle shining on a white surface that is 1 square foot in size and 1 foot from the candle.
Most vegetable plants need at least 1,000 footcandles, but many houseplants can get by with less. Many of our houseplants originated on shady rainforest floors, so are adapted to low light levels. Taller plants tend to require more light than small, bushy ones.
In geographic areas with chronic low light or long winters, you can use fluorescent or other plant lights to supplement natural sunlight. High-intensity discharge lamps such as high-pressure sodium or metal halide are expensive but efficient.

Air and Soil Temperatures

Air - Plant growth requires heat. Temperature determines how quickly plants take up water and nutrients, their rate of photosynthesis, and their growth. Maintaining a comfortable air temperature for your plants can be a challenge. Generally, 50 to 60°F is a minimum temperature for greenhouse plants, while 85°F is the maximum. Plants generally do best with a 10- to 15-degree drop between day and night temperatures.
Tropical natives or food plants that produce edible fruits (e.g., tomatoes) can probably withstand higher temperatures. Plants native to more temperate climates, or those with edible leaves or roots (e.g., lettuce), typically prefer cooler temperatures.
Soil - Soil temperature is even more important than air temperature in your greenhouse, particularly if you're growing in beds. When soil temperatures are below 45°F, roots grow more slowly and are less efficient at taking up water and nutrients. Warm soil is particularly important for germinating seeds or rooting cuttings.
65 to 75°F is recommended for germinating most types of seeds. Have students use a special soil thermometer to monitor soil temperatures, and consider experimenting with growth rates of seedlings in warmed and unwarmed soils. You can supply bottom heat for containers by purchasing special soil heating cables or mats. Be sure to read the safety precautions carefully, and never try to adapt an electric blanket or heating pad for greenhouse use!

CARBON DIOXIDE: A BREATH OF LIFE

Carbon dioxide (CO2) is essential to the process of photosynthesis. If it's scarce, plant growth slows. If your greenhouse air is stagnant, plants can deplete the carbon dioxide in the layer of air surrounding the leaves, even though there may be plenty in the rest of the greenhouse. Keeping the air moving, via vents or fans, is important for providing necessary CO2 to plants. Some home and school greenhouse growers have tried increasing CO2 by composting right in the greenhouse, since the composting process produces carbon dioxide as well as heat. Consider challenging your students to invent other ways of providing CO2 (e.g., human breath or dry ice!) and experiment to examine its effects on plant growth.

Cooling

To maintain comfortable greenhouse temperatures, you may need to keep some light out of the greenhouse. Overheating problems are actually more common than underheating problems in greenhouses. Even in the North, a late spring temperature of 110° F has been recorded inside a greenhouse on a sunny day.
You can use various methods to block some of the sun's rays. These include:
·      hanging commercial shadecloth (made of spun or mesh vinyls) inside the greenhouse
·      applying water-soluble shading compounds to glazing during late spring
Remember that if you create shade to cut down on heat, your plants will also receive less light, and may grow more slowly.

Venting

Venting is critical both to draw out hot air and to provide air circulation to reduce problems with pests and diseases. Vents can be manual, electric, or solar (these are triggered to open and close by the heat of the sun.) Ideally, vents should be placed both high and low to allow for proper airflow. They should be well constructed so they can be tightly closed on the coldest days. Exhaust fans placed high in the greenhouse help push hotter (upper) air out, while allowing cooler (lower) air to enter.

Heating

Depending on your location and growing interests, you may need additional heating to supplement the heat generated through solar radiation. This adds to your expenses but allows you to extend your season. Use supplemental heating when the sun sets and the cold outside air begins to rob the greenhouse of its daytime warmth.
Forcing hot water through pipes on the inside perimeter is a conventional heating method. Combining a fan with a gas or oil heater or wood stove is another method for circulating warm air through the greenhouse. Be sure that whatever heating system you use is well vented and has a fresh-air intake.

Greenhouse Gardening

EXTEND YOUR GROWING SEASON OR EXPERIMENT WITH DIFFERENT PLANT VARIETIES

WHAT TO GROW, WHEN

What you choose to grow, and when, depends on your curriculum goals and student interests, climate, and the type of greenhouse you have. See Greenhouse Climates for more information on different types.
Generally speaking, a greenhouse that can maintain a minimum of 60°F at night can grow almost any crop year-round. Most school greenhouses have some limitations, but think of the greenhouse as a microclimate of your outdoor growing conditions. You will be more successful if you match the needs of the plants you grow to your particular greenhouse conditions, just as you would consider your hardiness zone for growing plants outside. It would be quite frustrating, for example, to attempt to meet the needs of a banana tree (which requires bright light and warm temperatures) in a cool northern greenhouse.
Below you will find some plant suggestions for your greenhouse. What you can grow varies seasonally. Remember to check for pests before bringing any garden plants inside.
Fall Possibilities
·      bulbs for forcing
·      lichen and moss terraria
·      seedlings of cool-season crops (Chinese greens, collards, lettuce, herbs) to put in greenhouse beds
·      plants retrieved from the garden--experiment by digging up some annual flowers, vegetables, or herbs to see what survives the change
Winter Stalwarts
·      plants harvested from the fall garden
·      forced branches of pussy willows, forsythia, apple blossoms if you have a heated greenhouse or live in a warm climate
·      tender perennials to overwinter if you have a cold greenhouse
·      nothing, if you have an unheated greenhouse in a cold climate
Early Spring Dandies
·      seedlings for outdoor gardens
·      herbs, vegetable plants, flower plants for plant sale
·      seedlings for warm-season crops (tomatoes, melons, cucumbers) to grow in greenhouse beds through the summer
Summer Sweeties
·      warm-season crops (tomatoes, cucumbers, eggplants, melons) in greenhouse beds, particularly in areas with a short growing season
·      perennials from seed or cuttings
·      tropical crops (figs, citrus fruits, bananas)

IF NOT BEES, WHO?

In nature, flowers are pollinated by insects, wind, birds, bats, and so on. Without natural pollinators in greenhouses, who does the work of moving pollen from the male to the female flower parts, so fertilization and fruit and seed production can occur? Fortunately, many crops that produce edible fruits or seeds have both stamens (male parts) and pistils (female parts) in the same flowers. Pollination occurs easily since the parts are arranged to facilitate pollen transfer. Greenhouse crops such as tomatoes, peppers, and beans are in this category. You can help pollinate them by shaking them gently from time to time. Special European varieties of greenhouse cucumbers are designed to bear fruit without pollination. If you and your students want to try to "play the bees," you can do so with regular garden cucumbers, melons, or squash.

Planting Options

GREENHOUSE BED GARDENING

Soil-filled greenhouse beds, near ground level or raised to 24 inches, are ideal for creating indoor planting habitats. Since beds (particularly raised) typically contain more soil than containers do, they promote good root growth.
The soil also provides thermal mass that retains some of the heat captured during the day. One disadvantage of using beds is that if you do have a problem with soil-borne fungi or other pests, you may have to dump an entire batch of soil to remedy the problem.
You can construct greenhouse beds from wood, bricks, stone, or recycled materials. Don't use pressure-treated wood or most wood treatments, since they often contain substances that can harm plants. Use either untreated hardwood or wood treated with a plant-safe preservative containing copper napthenate. If the beds will be accessible only from one side, build them no wider than 2 1/2 feet. They can be somewhat larger if students will be accessing them from two sides.

CONTAINER GARDENING

If you're growing in containers, conventional plant pots or recycled materials like cardboard milk cartons or yogurt containers will do the job, as long as you put holes in the bottom for drainage.
Unglazed clay pots are good because they're porous; however, they are heavy and breakable. Plastic pots, on the other hand, are lighter and easy to clean, but can be more easily over-watered.
Clean containers well to avoid pest and disease problems. Soak them for 1 hour in a solution of 1 part chlorine bleach to 9 parts water, or use warm soapy water.
Be sure that the container size is appropriate for the plant you're growing. A vegetable plant in a pot that's too small for it will be stressed and susceptible to attack by disease organisms and pests. On the other hand, a plant in a pot that's too large will also grow poorly, because it may get over-watered.

Growing Media

Soil found outside stores and releases nutrients, provides plant support, and creates passages for air and water. It contains living thing--bacteria, mites, and worms, as well as nonliving substances--small particles of sand and clay. Greenhouse soils need to be lighter than garden soils, because frequent watering tends to pack soil down. Many greenhouse growers use soil-based or soilless mixes that have been heat-sterilized so they contain no living organisms such as fungi, weed seeds, or insects that thrive in an inviting greenhouse environment.

MIXES FOR CONTAINERS

We recommend using a commercial soilless mix (available at garden centers, nurseries, and hardware stores) for starting seedlings, which are particularly susceptible to disease and require a light medium that holds moisture well.
If you and your students are adventurous, you can make a soilless medium yourselves:

SOILLESS RECIPE

Mix in equal parts:
·      Canadian peat moss
·      perlite
·      vermiculite
Although good for starting seeds, these soilless mixes are low on nutrients and tend to dry out quickly. For larger plants, you should find a heavier commercial potting soil that contains some sterilized soil or organic material.

MIXES FOR BEDS

If you're growing in beds, it's best to provide a soil mix that closely approximates soil found outdoors. If your outdoor soil is heavy, you'll need to improve its drainage for use in the greenhouse. Adding compost, peat, or other organic matter to the soil helps with this balancing act.

SOIL FOR BEDS RECIPE

Mix in equal parts:
·      rich soil
·      organic material (peat moss, leaf mold, or screened compost)
·      drainage material (sand, vermiculite, perlite)
You'll also need to check and adjust the pH (to keep it between 6.0 and 6.8) and may want to add other mineral amendments (e.g., bone meal) to provide additional nutrients.
When filling beds, first lay down a few inches of gravel and a few inches of sand on the bottom for drainage, then add 1 1/2 feet or more of your soil mix.

Nutritionally Speaking

Plants require certain nutrients in order to thrive and grow. These are not actually food, but chemical elements or minerals that are vital to helping a plant use the sugars (the real food) that it produces during photosynthesis. Nutrients are normally found in soil, in decomposed organic matter such as compost, and in commercial fertilizers. The "macro-nutrients"--those required in the greatest amount by plants--include nitrogen, phosphorus, and potassium. Micro-nutrients such as iron, sulfur, and zinc are also required by plants, but in smaller quantities.
Garden soil and organic matter in greenhouse beds provide some nutrients to the crops. You may want to side-dress plants with compost or other fertilizer from time to time as you would plants in an outdoor garden. Container-grown plants require more frequent fertilizing than those grown in greenhouse beds, particularly if you're using a soilless or nearly soilless potting mix. You can fertilize plants in containers with commercial liquid or water-soluble fertilizers, or slow-release pellets.
Whether using organic or synthetic fertilizers (you may want to compare different types), look for those containing micro-nutrients, and follow directions on containers. Because plant needs are so interconnected, plants tend to require more nutrients during the summer when they receive more light and heat, and fewer nutrients in the winter.

Starting from Seed

You and your students will want to start some seeds in their permanent containers or beds, if you are raising crops that do not transplant well (such as beans, peas, cucumbers, melons, squash, carrots, beets, and radishes) or if transplanting them later on isn't an option. You may choose to sow other seeds in temporary containers, and later transplant them to larger containers or greenhouse beds. This saves space, allows you to choose only the healthiest seedlings, and involves students in an important and exciting gardening activity.
If you're growing vegetable crops to maturity in the greenhouse, look for designated greenhouse varieties that are designed to:
·      be more heat tolerant
·      resist certain diseases
·      produce fruits without being pollinated

PEAS GROWING HIGH IN THE SKY

by Lisann Zentner 
First grader at Columbia School, Seattle, WA
Peas growing high in the sky. 
How delicious. 
I can imagine you and me eating those yummy peas. 
They're coming soon. 
They're growing tall on a vine ripe as can be. 
I can see you and me having a picnic as fun as can be. 
With only those yummy peas. 
I can't wait, how about you?

Planting Tips

·      Use a disease-free, well-drained soilless mix and clean pots for sowing seeds.
·      Moisten the mix well and fill containers to within 1 inch of the top.
·      Plant seeds at a depth of two to three times their width.
·      Plant seeds that are very fine, or require light, by sprinkling them on the surface and gently patting them into the soil.
·      If sowing seeds directly into their permanent containers, space the correct number of seeds evenly around the container; put two seeds in each planting hole to ensure germination.
·      If sowing seeds for later transplanting, space seeds about 1/4 inch apart in rows 1 to 2 inches apart.
·      Keep soilless mix moist while seeds are germinating by covering the container gently with a plastic bag or dome.
·      Keep containers in a warm spot (70 to 75°F), or use heating mats or cables to maintain warmth.
·      Once seedlings emerge, immediately put them in the light. If germinating them under fluorescent lights, keep lights 1 to 3 inches from seedlings.
·      Thin or transplant seedlings once they have their first true leaves, so they don't compete for resources.
·      Fertilize the seedlings once six to eight leaves have emerged.

Starting from Cuttings

  "Another student, streetwise and courting trouble with the law, sold cyclamen and poinsettias at a community holiday open house. In talking with the community, 'keeping the buck change' on $4 plants paid for with a $5 bill, and being the 'plant expert,' he began to recognize the community and a place for him within it," marvels Sandy May-Fitzgerald, a special education biology teacher in Danbury, CT.Propagating plants from parts of other plants is a relatively easy way to increase your collection quickly and to engage students in investigating vegetative propagation. Many common houseplants will root nicely in a greenhouse environment. Rooting stem cuttings from tomatoes can also be fun to try. Depending on the plant, you can take stem, leaf, or plantlet cuttings. Consider taking stem cuttings of some of the following:
·      begonia
·      coleus
·      geranium
·      impatiens
·      ivy
·      philodendron
·      tomato
·      wandering Jew

TIPS FOR STEM CUTTINGS


·      Select a healthy, well-watered parent plant and take a 3- to 5-inch cutting from a new tip.
·      Remove all but the top few pairs of leaves.
·      Fill a container with moist soilless mix, and poke holes at least 1 inch apart to accommodate cuttings.
·      Carefully place each cutting in a hole and close up the hole. (Some people dip cuttings in a commercial rooting hormone, available in many garden centers, to speed rooting and prevent the stem from rotting.)
·      Place individual containers in plastic bags propped up with stakes or under plastic domes and seal them to retain moisture.
·      Keep the containers in a warm area in the greenhouse, and check them occasionally to ensure there is adequate moisture.
·      After a few weeks, tug gently on the cuttings to see if they've rooted. When you feel resistance, they're ready for transplanting.
·      Gently separate the cuttings and move them to individual pots.

Watering

Watering is an ongoing challenge for school greenhouse growers. Water is the solvent that carries minerals from the soil to plants via the roots. A raw material used in photosynthesis, water enters the roots as a liquid and exits the leaves as a vapor as it's transpired.
The amount of water plants require is affected by the drainage capacity of the growing medium used, the temperature and light plants receive, the amount of air circulation, the stage of plant growth, and the type of plant. Young, actively growing seedlings, for instance, require constant moisture, while a mature cactus needs very little.
Over-watered plants are at just as much risk as those that are under-watered. (Sometimes over-watered plants wilt as their roots suffocate, leading us to think they need even more water!) Have students practice "reading" the plants by using a finger to check moisture levels. If the soil feels dry an inch down, it's time to water. Don't necessarily water out of habit or on a schedule; water when the plants need it.

WATERING TIPS

 
·      Use slightly warm (65 to 80°F) water.
·      Water in the morning to minimize evening condensation on leaves, which can encourage diseases.
·      Minimize watering on cool, cloudy days.
·      Be careful not to splash mud, damage seedlings, or get water on fuzzy-leaved plants.
·      Be sure to water thoroughly. Watering too lightly can cause a buildup of fertilizer salts, which can be toxic to plants, and also stimulates shallow, surface roots at the expense of larger roots.

Humidity

Humidity is essentially how "wet" the air is. Hot air holds more water vapor than cold air. Most plants do best with a relative humidity (the percentage of the amount of water that the air can hold at a given temperature) of between 45 and 60 percent. High humidity leads to pest and disease problems and causes vapor to condense when warm water-filled air hits a cold surface. Low humidity, on the other hand, can dry out plants. Transpiration from plant leaves contributes greatly to greenhouse humidity. To avoid excessive humidity, water early in the day and only when needed, and make sure you have good greenhouse ventilation. If your humidity is too low, you can raise it by periodically wetting down the floor or misting plants.

Pests & Diseases

WHEN TRYING TO KEEP UNWANTED VISITORS UNDER CONTROL, THE FIRST STEP IS TO RECOGNIZE THE ENEMY

In general, there will be attempts by other organisms to colonize the greenhouse paradise you have created. After all, if you were a whitefly or an aphid, wouldn't you rather spend the winter in a warm, moist, verdant spot than in a hard egg under a frozen log? When dealing with pest problems, take heart in the fact that plants often survive pest and disease attacks and that such events can lend another dimension to your students' investigations.

PREVENTION: THE BEST MEDICINE

Healthy plants are the best defense against greenhouse pest and disease problems. Here are some tips to help you prevent problems before they start:
·      Keep it clean! Promptly dispose of all trash, plant parts, diseased plants, and plants past their prime so they won't invite problems.
·      Inspect plants carefully and quarantine the newcomers for a few weeks before putting them in the greenhouse.
·      Have children wash hands with soap and water after handling diseased plants.
·      Make sure your hose doesn't become a disease spreader; keep it from direct contact with plants and keep the nozzle off the floor.
·      Start with fresh planting media each season.
·      Scrub and rinse the greenhouse interior from top to bottom with a warm disinfectant soap solution at least once a year.
·      If your greenhouse is empty during the winter, you may want to do a "freeze-out"--let the inside temperature plunge to wipe out remaining pests.
·      Keep air circulating and plants dry. High humidity (above 70 percent) and stale air encourage many pests and diseases. Good ventilation and even small circulating fans can make a big difference.
·      Give your plants the recommended amounts of water and fertilizer. A deficit or excess can stress plants and invite problems.

Greenhouse Pests 101

What types of visitors can you expect? Some of the most common greenhouse pests are aphids, whiteflies, and spider mites.
In the early stages of infestation, your students can handpick and squash problem pests. For larger infestations, you might try a diluted solution of insecticidal soap sprayed on the entire plant, especially leaf undersides. You can purchase these commercially or use mild dish liquids or soaps like Ivory Liquid (3 to 6 tablespoons per gallon of water). If you have a bad infestation, spray every 3 to 5 days, first testing the solution on a small portion of a leaf. While soap sprays can be effective with a range of pests, they can also harm the good ones, so use them judiciously.

Common Greenhouse Pests

Common greenhouse pests include:
Pests
Description
Control
Aphids
Small, pear-shaped insects with long legs; often pale green to white; may be winged or wingless; secrete a sticky honeydew; found on new buds, rapidly growing tips, underside of leaves near veins; they suck plant juices, reducing vigor, stunting plants, and transmitting diseases.
Squashing; heavy spray of water; soap spray; homemade spray; predators (brachonidwasps, certain predatory midges, green lacewings, ladybugs).
Spider Mites
Nearly microscopic (less than 1/16 inch) arthropods with four pairs of legs as opposed to an insect's three pairs; create webbing strung between the leaf and stem; damage appears as leaf mottling; thrive in hot dry seasons and prefer foliage plants.
Repeated heavy spray of water; predators (predatory mites).
Whiteflies
Tiny, delicate, white-winged insects that feed on a wide range of plants; in large numbers, they'll rise up in a white cloud when disturbed; immature stages look like transparent to opaque white dots on underside of leaves; adults congregate on tips; damage similar to that of aphids.
Soap spray; yellow sticky traps; predators (Encarsia formosawasps).

Some schools also report success after carefully experimenting with homemade sprays containing hot pepper, garlic, and other strong substances. A number of greenhouse pests, particularly whiteflies, can be lured to yellow boards or cardboard hung throughout the greenhouse and covered with Tanglefoot, a thin layer of axle grease, or another sticky substance. Natural predators or biological controls can discourage populations of certain greenhouse pests. Ladybugs, praying mantises, and other beneficial insects, if properly introduced, can keep pest populations down, and can provide fascinating fuel for investigations

School Stories

FIVE STORIES OF SUCCESSFUL SCHOOL GREENHOUSE PROJECTS

 

Most school greenhouses become cornerstones of larger outdoor gardening initiatives. Whether a parent, teacher, principal, or superintendent drives the process, however, all involved should consider carefully the scope and sustainability of a greenhouse project. Separating startup costs from ongoing costs is helpful; most successful greenhouse programs generate their own ongoing funds through plant sales or sustaining school or grant funds.
Community support is another element of successful greenhouse and gardening programs. Through donations of raw goods (such as lumber, pots, or seeds), volunteer effort and expertise, parental involvement, and financial donations and grants, greenhouses and gardens can sprout into patches of community pride. Sending food home with kids or to the cafeteria, selling or donating plants, and offering thriving indoor and outdoor habitats are powerful elements of community beautification, bonding, and transformation.
Because greenhouses are artificial environments where every factor is controlled, they are ideal for inquiry-based learning. Educators who find ways to collaborate successfully and take time to integrate greenhouse and garden work into the curriculum are likely to enjoy ongoing prosperity. Greenhouse and garden projects that offer innovative ways to meet required educational benchmarks are also more likely to be funded appropriately.
Through the following profiles, discover how other educators and parents have established and continue to operate successful greenhouse and garden programs. Each program is as unique as the individual or school driving the effort, the local climate and bioregion, and the projected educational goals. And take heart. If you choose to initiate a greenhouse and garden program in your school, the possibilities--as the following narratives demonstrate--tend to blossom as you go along.

Greenhouse Support

GARNERING FINANCIAL SUPPORT

WAYS TO KEEP YOUR GREENHOUSE GOING INTO THE FUTURE

If you're constructing or refurbishing a greenhouse, you'll need significant funds for site work, consultants, construction, interior supplies, and so on. One school received construction start-up money through a federal safe and drug-free schools initiative. School and community representatives designed a program to help at-risk students work together to create and manage a small greenhouse business. Others have funded greenhouse projects through local foundation grants. To find funds to launch or provide long-term support for a greenhouse project, consider approaching some of the following sources:
·      community development block grants
·      community foundations
·      public school foundations
·      local corporations and businesses
·      service clubs
·      parent/teacher organizations

Locating Ongoing Funding

To secure funds for ongoing maintenance of the greenhouse, Julia Kirkwood, an environmental science technician in Kalamazoo, MI, recommends working greenhouse projects directly into the curriculum. "If you show how benchmarks are being met, the administration is more likely to support the work and provide maintenance funding," she states.
Once you have a greenhouse, you'll have ongoing needs for replacing supplies such as containers, potting mix, and seeds. Many schools have been challenged to think creatively about ways to obtain these supplies without making great demands on tight budgets. In some classes, students write letters or make presentations to managers of garden centers or other garden-related businesses. When you or your students solicit donations, be sure to explain your project and its objectives clearly. Describe how the donation will be recognized (for instance, through a donor recognition sign at the greenhouse entrance). As part of a presentation, remind companies that interested students could grow up to be lifelong customers. Also consider approaching the following groups for donations of new and used gardening materials:
·      botanical gardens
·      local garden clubs
·      university or city greenhouses
·      local service clubs
·      community garden groups
Be sure to follow up all donations with thank-you letters. If people know their gift was appreciated and well used, they are more likely to continue giving. Encourage your students to take this on. Heartfelt thank-you letters, children's drawings, and photos of abundant greenhouses with smiling faces are among the most valued ways of saying "thanks" to supporters. Maintain contact by sending donors any newspaper clippings or photos that highlight the project, and be sure to mention their contributions in any news stories or other publicity.

Plant Businesses

A number of schools use greenhouses to start plants and seedlings for special fundraising plant sales. These include garden vegetable, flower, and herb seedlings; houseplants from cuttings; and even Easter lilies and poinsettias. Typically, students are responsible for researching specific plant needs, projecting sales, starting and caring for plants, and promoting and staffing the sale. Rather than selling seedlings, some schools plant them to beautify local parks, senior centers, and other community locations. Others raise seedlings, marigolds, herb plants, or houseplants for Mother's Day or other holiday gifts.

Finding Volunteers

A greenhouse project is a great way to involve parents and other community volunteers in your school. Consider having students send letters to parents explaining the greenhouse project and encouraging them to visit and participate in special activities and events, or requesting support from those parents with relevant skills or expertise. Some schools hold open greenhouse days or plant sales in which students give tours and presentations. Parents who garden may be flattered by an invitation to talk to classes or lead an activity in the greenhouse. A school newsletter that highlights how the greenhouse is being used can keep parents informed. The greenhouse project might also attract a variety of other volunteers who have the expertise to diagnose a specific growing problem, conduct a session with your students, or help conduct teacher in-service workshops. Consider seeking volunteers through such groups as local garden clubs, botanical gardens, or the Master Gardeners' or 4-H program of your local county cooperative extension service.

Student Greenhouse Managers

In some school greenhouses there is a "manager," typically an adult who does most of the monitoring, watering, fertilizing, and other greenhouse management work. But other programs encourage students to become proficient at various aspects of monitoring, managing, and working in a greenhouse, and designing their own investigations stimulated by their own questions. With suitable support and references, they can assume responsibilities as caretakers and problem solvers.
An important part of successful greenhouse gardening (and one that will lead to a particularly important set of skills for students) is regular monitoring. Keep an air thermometer, a soil thermometer, a hydrometer (for humidity), a maximum/minimum thermometer, and record-keeping materials handy. Students will hone skills as they collect weather data and apply the information to managing the greenhouse. Encourage them to discuss how to maintain temperatures between 45 and 75° F, keep the humidity in a comfortable range, or otherwise maintain a plant-friendly environment.



Activities

·              Seasonal Sun
·           Microclimate Search
·           Water Wisdom
·           The Greenhouse Effect
·           Shadows and Light
·           Glaze Testers
·           Measuring Light Intensity
·           Shady Dealings
·           Mixed Media
·           Pest Sleuths

Seasonal Sun

Challenge older students to explore the sun's seasonal movements by determining the average height of the sun at noon in each of the school year seasons. Establish a viewing spot where observers can stand each time. Let the students decide how to record the path of the sun; for example, "it is three index cards above the tree at noon in September and two index cards above the tree in November." If you have a large window on a south-facing side of the school, students can mark the path of the sun for a day using adhesive dots, every 2 hours or so. This will establish an arched path across the window. Repeat this once each season using red dots for a "fall sun," another color for a "winter sun," and so on, then compare where the paths fall. It is important to establish a viewing spot that is used each time by observers of roughly the same height so the spots remain fairly accurate. Warn students never to look directly at the sun!

Microclimate Search

A greenhouse typically has many mini-environments, or microclimates. This is due to a variety of factors, including the following:
·      Hot air rises and cool air drops.
·      Air next to glazing is cold in winter and hot in summer.
·      Sunlight enters the greenhouse at different angles through the year.
·      Shade cuts down on light intensity.
Invite students to keep records to compare soil and air temperatures throughout the greenhouse. (A maximum/minimum thermometer can be a great teaching tool.) Where is the air warmest in the greenhouse? Coolest? Have them construct a map or chart to illustrate their observations and locate different microclimates within the greenhouse. Then use these environments to your advantage by researching plant needs and grouping plants according to where their needs are best met. (The best environment for a plant is usually determined by its native environment on the planet.)

Water Wisdom

Large greenhouse operations often determine water needs and use "automatic" watering measures, such as drip irrigation. Give your students some water-related challenges. For instance, ask them to design a simple self-watering system (perhaps with absorbent cloth wicks), a method of warming water before it's used on plants, or a "clue" chart to help one another decide when it's time to water.

The Greenhouse Effect

All greenhouses operate on the same basic principle. Radiant energy (light) from the sun can pass through transparent and semi-transparent materials. When the light arrives inside a closed space, it is absorbed by the surfaces within, then radiated again as thermal energy (heat). That energy is less able to pass through the transparent or semi-transparent materials, so the heat is trapped inside. Anyone who has entered a car parked in a sunny location knows what trapped heat feels like! This heat energy warms the air, enabling plant growth. As a simple but powerful exploration of this phenomenon, invite students to place a thermometer inside a clear, closed glass jar in the sun. Place a second thermometer next to the jar. After half an hour, compare the two temperatures. Your students may be surprised at the difference between the two readings.

Glaze Testers

Have students contact companies and request samples of their glazing materials. Then ask students to design a series of tests to evaluate key factors for each product and make recommendations for the greenhouse. They might investigate ways to measure light passage, strength, flexibility, heat-trapping characteristics, static resistance, and so on.
Have students contact companies and request samples of their glazing materials. Then ask students to design a series of tests to evaluate key factors for each product and make recommendations for the greenhouse. They might investigate ways to measure light passage, strength, flexibility, heat-trapping characteristics, static resistance, and so on.

Measuring Light Intensity

Your students can use a light meter in a manual camera to roughly measure light intensity in footcandles in different parts of your greenhouse. Here's how. First, set the film speed at ASA 200 and the shutter speed at 1/125 second. Aim the camera at a white sheet of paper in the greenhouse. Get close enough so the meter records only the light reflected from the paper (be careful not to create shadows). Focus on the paper and adjust the f-stop until a correct exposure shows in the light meter of the camera. F-stops will equal approximate footcandles as follows:
F-stop
2.8
4.0
5.6
8.0
11
16
22
Footcandles
32
64
125
250
500
1,000
2,000


Shady Dealings

Ask your students to investigate the effect of shade on temperature. Angle a piece of clear plastic or glass toward the sun, and record the temperature underneath. Then shade it with a piece of cloth or netting and repeat the investigation, comparing temperature readings. Try other methods of shading and compare them.
Ask your students to investigate the effect of shade on temperature. Angle a piece of clear plastic or glass toward the sun, and record the temperature underneath. Then shade it with a piece of cloth or netting and repeat the investigation, comparing temperature readings. Try other methods of shading and compare them. Have students speculate on how shading might affect the greenhouse climate, both positively and negatively.

 

 

Mixed Media

Challenge students to explore the effects of various growing media on plant growth. Have them set up a series of containers with different growing media, then plant the same type and number of seeds in each pot. What do they observe over time? Which medium dries out most quickly? Which one supports faster or better plant growth?

Pest Sleuths

Have students observe, sketch, and try to identify and categorize the different organisms in your greenhouse. Which pests seem to have which plant preferences? What types of environmental conditions seem to attract different organisms? Invite students to research and investigate the life cycles and needs of common greenhouse pests and beneficial insects, then have them use this information to invent ways to reduce pest numbers. Find out how commercial growers deal with pest problems. Research and debate the use of chemical versus biological approaches.



Exploring Classroom Hydroponics

What, No Soil?!
Hydroponics, in its simplest form, is growing plants by supplying all necessary nutrients in the plants' water supply rather than through the soil. The word derives from the Greek root words hydro andponics, meaning water working. Growing plants hydroponically helps gardeners and farmers grow more food more rapidly in smaller areas (greenhouses, living rooms, classrooms, and rooftops, for instance) and to produce food in parts of the world where space, good soil, and/or water are limited.
When youngsters explore how to grow plants hydroponically (without soil), fruitful questions bloom: How can we provide support for plants without soil? How do plants grown with just water and nutrients compare with plants grown in soil? How can we get the tallest plants using a hydroponics setup? These types of questions can lead to active investigations and problem solving. Record-keeping becomes a natural outgrowth of these endeavors. Concepts related to basic plant parts and needs, nutrition, food production, recycling, agricultural technology and other areas come to life in these soilless growing environments. These studies may even lead to classroom business opportunities or fuel student career interests. Not the least of the benefits is the joy of students harvesting a crop of their own incredible edibles!
This guide features a synthesis of information from hydroponics experts and from people who have explored hydroponics with children in classrooms. It presents basic how-to information, suggestions for helping students discover concepts through investigations, plans for simple hydroponics setups, and stories from classrooms where students and teachers have investigated this growing technique.


(Green) Thumbnail History

Records show that plants have been grown without soil for many thousands of years. The hanging gardens of Babylon used hydroponic techniques. Marco Polo observed these systems in China. To escape enemies, the ancient Aztecs reportedly took to the lakes and maintained large floating rafts woven of rushes and reeds on which they raised food crops. In 1699 the British scientist John Woodward grew plants in water to which he added varying amounts of soil. He concluded that while there are substances found in soil that promote plant growth, the bulk of the soil is used for support. By the late 1800s, horticultural scientists were successfully raising plants in solutions of water and minerals. The modern science of hydroponics began in the 1930s when Dr. W. E. Gericke at the University of California raised tomatoes and other crops on floating rafts, applying the earlier principles in a commercially successful way. He coined the name hydroponicsas he worked with water. What more can your students discover about the history of soilless growing?

WATER, WATER

Did you know that most plants are composed of about 90 percent water? It's an essential component of photosynthesis, necessary for normal cell function, and is the medium in which nutrients are transported throughout the plant. Plants need water in different amounts during different growth stages. A large cucumber plant, when fruiting, can use up to a gallon of water a day! (Transpiration uses up the majority of a plant's water intake.) In hydroponics, water with dissolved nutrients is applied as a bath, periodically irrigated through the growing medium, or sometimes sprayed directly on the roots.

Meeting Plant Needs

THE NITTY GRITTY WITH NO GRIT!

Plants, like all living things, have certain requirements that need to be met for them to grow and thrive. These include water, nutrients, light, air, and structural support for the roots. In traditional gardening, plants get root support, nutrients, water, and oxygen from the soil. Without soil, hydroponic growers must find ways to provide water and the right balance of nutrients directly to the plants' roots, enabling the plants to concentrate their energy on producing leaves and fruits rather than searching for water and nutrients. Another challenge is designing ways of providing the support and oxygen that plants need. Before reading more about plant needs and some of the innovative ways hydroponic gardeners meet them, read this refresher on plant plumbing.

ROOTS AND SHOOTS

The most important function of plant roots is to absorb water and nutrients. How does it happen? Covering the growing tip of each root are hundreds of tiny root hairs. The cell walls and membranes of the hairs are porous thereby allowing water molecules containing dissolved minerals to enter. The movement of the molecules through the cell membranes is called osmosis. Osmosis occurs because the water seeks balance in the concentration of nutrients inside and outside of the plant.
Plant roots deliver the necessary water and nutrients (via the stem) to the plant's leaves where photosynthesis -- food (energy) production-- occurs. During photosynthesis carbon dioxide enters the plant through the leaf's surface. Carbohydrates (glucose) are produced from carbon dioxide and a source of hydrogen (water) in chlorophyll-containing plant cells when they are exposed to light. This process results in the production of oxygen. (Like animals, plants also require oxygen for respiration.) These carbohydrates fuel plant growth and reproduction. Only a small amount of the water sent to the leaves is used in photosynthesis; the rest is given off into the air through transpiration.
You can explore the phenomenon of osmosis with your students by inserting a clear straw into the hollowed-out top of a fresh carrot, dripping candle wax around the straw to serve as a seal. Set the carrot in a jar of water, then drop a small amount of sugar water down the straw and mark its position. Students should be able to see the fluid in the straw, which simulates the carrot stem, rising under osmotic pressure.

Nutritionally Speaking

Whichever type of hydroponic system you select or create, you must supply the plants with nutrients. In soil, these elements come from rock and mineral leaching and organic matter decomposition. They are "held" by the soil particles and dissolved in the surrounding water. In hydroponics, the liquid solution is taken in directly by the roots and provides the leaves with nutrients through the transportation system in the stem. These nutrients or minerals are not actual food, but elements vital to helping the plant utilize the sugars (the real food) that it produces during photosynthesis.

IMPORTANT NUTRIENTS

Plants need about 16 different essential elements for optimum growth. Macronutrients, which are ordinarily found in soil, are needed by plants in rather large amounts. (Hydrogen, oxygen, and carbon are also necessary in large amounts, but are available to plants from the air and water.) The following are essential macronutrients:
·      nitrogen (N) - Promotes development of leaves
·      phosphorus (P) - Aids in growth of roots
·      potassium (K) - Helps plant resist disease
·      calcium (Ca) - Helps promote new root and shoot growth
·      magnesium (Mg) - Contributes to leaf color and helps absorb sunlight
·      sulfur (S) - Contributes leaf color
Trace elements, or micronutrients, including manganese, iron, copper, and others, are important to the total well-being of the plant, but in much smaller amounts.

CLASSROOM TIPS: SUPPLYING NUTRIENTS

Hydroponic gardeners provide plant roots with a nutrient solution containing an appropriate balance of necessary nutrients -- a "super nutrient soup," suggests one fifth grade teacher. The easiest way to supply them is to purchase prepared hydroponic nutrients in dried or liquid form. Most are concentrated and must be mixed with water. Some classrooms have used commercial houseplant fertilizers for hydroponics, with mixed results. Students may want to compare the effects of different types of fertilizers on plant growth. Upper-grade students might want to experiment with varying proportions of individual nutrients to make their own "super secret soup."
Mixing Solutions - When mixing nutrient solutions, always dilute them to the concentration recommended by the manufacturer, typically 1 or 2 teaspoons per gallon of water. Water between 65 and 75 degrees F makes nutrients most available to plants. Tap water may contain significant concentrations of chlorine, which can adversely affect plant growth. If your water has a lot of chlorine, you can use distilled water or simply let water stand uncovered for a couple of days before using it. Your students might want to explore this themselves by comparing plants grown with distilled- versus tap water-based nutrient solutions.
How Much to Use - The amount of nutrient solution you use depends on the type of system, temperature, light, and other factors. If you're growing plants like lettuce, herbs, or flowers in a simple system such as a floating raft, a good rule of thumb is to provide 2 quarts of nutrient solution per plant. If you're trying to raise larger, fruiting crops in a more sophisticated system, you'll need to supply closer to 2 gallons of nutrient solution per plant.
Maintaining Nutrients - You'll have to replace the nutrient solution at different intervals depending on the type of system you set up, because nutrient concentration will vary as nutrients are taken up by the plant and as water evaporates and transpires from plant leaves. (Commercial growers use special equipment to measure the concentration of nutrients in a solution.) A good general rule for most classroom systems is to replace the mixture with a fresh batch every 10 to 21 days. Invite students to consider ways in which these solutions can be recycled, such as by watering other classroom or outdoor plants. As the water in your system evaporates and transpires, you may also want to top off the solution with more water to avoid building up concentrations of mineral salts.
Nutrient Disposal Caution -Take care where you dispose of nutrient solutions. Houseplants, indoor plants, and container gardens are fine places to recycle the liquid. However, aquatic ecosystems are quite sensitive and the balance of minerals is very delicate. If there is a stream, lake, or other water source nearby, do not dispose of liquid nutrients on the ground.

pH: The Acid Test

The pH of the nutrient solution is an important factor in hydroponics. It is a measure of the acidity and alkalinity on a scale from 1 to 14, with 1 being very acidic, 7 being neutral, and 14 being very alkaline. Most of the plants in your classroom hydroponics projects grow best when the pH of the nutrient mix is between 5.8 and 6.5. At pH readings above or below this range, certain nutrients become unavailable to plant roots. The range that allows the plant to use the dissolved minerals most effectively is just slightly acidic. pH levels vary in different nutrient mixes and water sources. If you change your nutrient solution every 10 to 21 days, as suggested, you needn't be concerned with adjusting pH, but doing so can be an engaging focus for students. You can use narrow-range pH paper, reagent type test kits, or a pH meter to do so. (Check with aquarium suppliers or science supply catalogs.) In the classroom, drops of white vinegar can lower the pH while baking soda can raise it. Hydroponic suppliers offer other products for adjusting pH.

Mixed Media

The material that a plant lives in or on is called itsmedium or substrate. For most plants, the medium is soil. Hydroponic growers find other ways to support growth to prevent drowning plants. Many setups use an inert, sterile medium. Some of the more popular choices included gravel, clean sand, perlite (a lightweight expanded mica), a lightweight pebble-likeaggregate, and rockwool (an inorganic, spongy, fibrous substance that holds large amounts of water and air). These materials provide passages among the particles or fibers where air and water can circulate.
Each medium has strengths and weaknesses. Gravel and sand, for instance, provide support and good drainage, but can be heavy when wet and will dry out fast. Perlite is light and holds water well, but its fine dust can irritate lungs. (Sprinkle it lightly with water to avoid this.) Rockwool holds water and air nicely and makes it easy to move plants around, but breaks down fairly quickly. Your student scientists will benefit from exploring the properties and performance of a range of standard media and inventing some of their own.
Some hydroponics systems have no real media, but more or less elaborate ways of suspending plants in nutrient solutions. In commercial nutrient flow technique (NFT) and aeroponics, for instance, the roots lie or are suspended in a dark channel and nutrients are sprayed or trickled along the root zone.

CLINGY PLANTS  

 

Many plant species grow naturally without soil. Challenge your students to find out more about epiphytes, plants that grow on other plants, particularly in tropical forests. What are they? How do they survive? Where do they get their nutrients, air, and water? Why are they important to the total biosphere?

A Breath of Fresh Air: Getting Oxygen to the Roots in the Garden

It is sometimes difficult for students to realize that even roots buried in soil must have oxygen for the plant to survive. Plants respire by taking in oxygen, which triggers plant cells to release and use the energy manufactured during photosynthesis, while also releasing carbon dioxide and water. Plant roots typically take in oxygen that's available in the small spaces between soil particles.

CLASSROOM TIPS: SUPPLYING OXYGEN

Hydroponic systems often use a pump to infuse oxygen into the water. For small setups, such as the Soda Bottle system described in this guide, aquarium pumps do the trick. In some systems (particularly commercial ones), the growing medium and roots are periodically splashed or flooded with a nutrient solution, allowing oxygen to bathe the roots in the interim.
In short-term passive systems, there are other means of getting oxygen to the roots. In some setups, water and nutrients reach the roots via a wick made of absorbent material, and part of the roots are continually exposed to air. A porous medium like rockwool has a tremendous capacity for retaining oxygen while also absorbing nutrient solutions. In systems like the Simple Straw Aeration described in this guide, human bubbles do the aerating! Greens such as lettuce and herbs seem to be the best bets for a minimally aerated environment.

AIR . . . WHERE?

To explore how much air can be contained in soil, have your students place a measured amount of coarse sand in a beaker or graduated cylinder. Ask them to determine how much water they can add before the water begins to puddle at the top, and to note the air bubbles that come to the surface as the air is displaced by the water. The volume of the water absorbed is an indication of the volume of air previously contained in the soil.

APPLICATION TO THE SCHOOL GARDEN

Now that your students have a better understanding of the volume of air in the soil, have them think about what happens when portions of that air space in the soil is taken away. The roots have less air and won't be as healthy which consequently means, the plant won't be as healthy. Have your students think of ways the air spaces in soil may be taken away by humans. Some examples include compacting the soil by walking on it, overworking the soil, and overwatering. It is important that we, as gardeners, understand how to care for our plants from the ground up!

Let There Be Light

All green plants require light to drive the process of photosynthesis. The higher the light level, the potentially larger your hydroponic harvest, as long as you're adequately meeting other basic needs. If your plants are getting leggy or not growing, the light source is the first factor to check. Keep a close eye on how your plants are responding to light and adjust exposure accordingly.

NATURAL LIGHT

The sun radiates the full spectrum of light essential to plant life. A greenhouse is a great natural light source for growing hydroponically. A sunny windowsill will suffice for many non-fruiting vegetables, herbs, and flowers if you place your hydroponic unit 1 or 2 feet away from the glass. In climates with a lot of sunlight, make sure your plants get at least four hours per day of shade.

ARTIFICIAL LIGHT

Fluorescent lights hung in a GrowLab or other setup will suffice for certain crops if kept on 14 to 16 hours per day. While many houseplants and smaller plants with low light requirements (e.g., seedlings, lettuce, or herbs) will thrive in a hydroponics setup under fluorescent lights, commercial hydroponic gardeners and home gardeners wanting to grow larger fruiting and flowering light-loving crops (e.g., tomatoes) to maturity often use special high-intensity discharge lights with metal halide or high-pressure sodium lamps. These provide bright, efficient light closely approximating sunlight, but are significantly more expensive than fluorescent lights. Don't be discouraged from trying tomatoes, peppers, and other fruiting crops under a fluoresent light setup; students in many growing classrooms have done so successfully!

LUMINOUS LESSONS

Your students' curiosity might lead to controlled investigations of light intensity or duration. For example, they might ask: How many hours of light will produce the fastest growth rate? If you use a classroom windowsill, in which plants receive light primarily from one direction, your class may notice the plants' gradual bending toward the light, a response known as phototropism. Consider rotating the units every couple of days, if practical, and using the phototropic response to fuel investigations.

Planting Advice

SOWING AND GROWING SANS SOIL

You will raise most of the plants for your classroom hydroponic garden from seed, but you can start houseplants and many herbs for cuttings of mature plants. If you have a simple system without pumps or other forms of aeration, your best bets are the following:
·      lettuce
·      beans
·      houseplants
·      annual flowers such as marigolds, zinnias, nasturtiums
If you have a more sophisticated active or commercial system, you might also try these crops:
·      tomatoes
·      cucumbers
·      bell peppers
·      corn (in tubes)

GROWING FROM SEED

You can start seeds in cotton, cubes of rockwool, peat plugs, perlite, or sand. After planting seeds, check regularly to make sure seeds remain moist, but are not water logged or moldy. If they are too wet, there may not be enough air for seeds to germinate properly. Some seeds, like beans and corn, will germinate in just a few days. Some others, such as tomato, bell pepper, and herbs may take as long as two weeks until they appear. If you do not see any sign of life after two weeks, it is best to replant the seeds.
After the true leaves form and a seedling is from one to several inches tall, you can transplant it into your system. Transplanting a seedling can be very stressful for a plant. Gently and carefully remove the plant, taking care not to damage the roots. A seedling, when transplanted into a bigger growing unit, is stressed at first. Some hydroponic gardeners recommend starting with half-strength nutrient solution, or initially spraying the leaves with nutrient solution rather than spraying or submerging roots, to minimize stress.

GROWING FROM CUTTINGS

Houseplants such as coleus, tradescantia, heartleaf philodendron, pothos, and geranium grow quite well from cuttings. Rockwool cubes soaked in a 25 percent nutrient solution are nice for starting cuttings. You can also use moist perlite or sand. Cuttings root more quickly if they're covered with a plastic dome or misted regularly to maintain a humid environment.

A FEW PLANT CARE TIPS

As with plants grown in soil, your hydroponic unit seedlings and cuttings require ongoing care. Here are a few general suggestions:
·      Plan space accordingly. Leafy and vining plants need room to spread out; provide support or trellising for such plants as tomatoes and cucumbers.
·      Grow disease- and pest-resistant plant varieties. (Good growing practices should minimize disease and pest problems.)
·      Practice good hygiene.(Without soil to filter contaminants, the liquid solution can transport impurities.) Wash hands before and after working with plants. Start with clean containers (a cleaning solution of 1 part bleach to 9 parts water is recommended).
·      Observe plants carefully for signs of insect pests. Aphids, spider mites, and white flies go for lush growth. Either hand-pick pests, wash plants gently with a mild soap
·      Change the nutrient solution regularly. Depending on the type of system you're using, you should change the nutrients every 1 to 3 weeks or so. Try to keep the pH between 5.8 and 6.5, the water temperature at around 70 degrees F, and the reservoir full.
·      Plan ahead for vacations. If the setups are small enough, you might send hydroponic gardens home with students. If your unit is large and has an automatic aeration/circulation pump, it can be left running, but be sure to let someone know it is on. Make sure the nutrient solution container is filled before you leave, and that automatic lights are correctly working on a timer. Some schools plan hydroponics projects to coincide with semesters or terms, to avoid the problem altogether.

Hydroponic Systems 101

A JOURNEY THROUGH THE TERMS AND DESIGNS

So, you're intrigued by the concept of sowing and growing sans soil, but not sure what type of setup makes sense. This section gives an overview of some general types of commercial and homemade hydroponic systems suitable for the classroom. If you want to do short-term explorations, raising crops like lettuce, herbs, houseplants, or annual flowers, consider a basic system like those pictured in Simply Super School Setups. If you have visions of producing mature fruiting plants like tomatoes, cucumbers, and so on, consider purchasing acommercial hydroponic unit or finding a design for a more sophisticated unit. There are a range of designs for hydroponic systems. Some use media, while others use only water. Some recycle nutrient solutions, while others rely on regular flooding with fresh solution.
The following descriptions and pages explain key hydroponic system terms and some general types of systems used commercially and by home gardeners.

PASSIVE SYSTEMS

These systems use no energy to move nutrients and water. They can be as basic as a perlite-filled flowerpot that is hand-watered regularly with nutrient solution. Passive systems often use a "wicking" material to draw up the liquid nutrients, or they simply suspend the plants in the solution with an air space around some of the root zone. They can be media-based or pure water-culture systems.

ACTIVE SYSTEMS

A hydroponic system is active if it relies on some type of energy (usually electricity via a pump) to move the nutrients in and out of the root zone area and to provide aeration. These systems, which can also be either media- or water-based, are generally used for larger plants (e.g., tomatoes and cucumbers) and tend to be more sophisticated. In recirculating or recycling systems, the nutrient solution is conserved by being recirculated either manually or electrically through the medium. These systems require closer monitoring of pH, nutrient concentration, and so on. Systems with pumps to aerate and deliver more oxygen to roots tend to produce healthier plants more quickly than do passive systems.

Media-Based Systems

These types of hydroponic systems rely on some material, such as gravel, aggregate, perlite, vermiculite, or rockwool to support the plants and the roots in the nutrient solution. Such systems can be active or passive and may or may not recycle the nutrients.
Following are descriptions of some common types of media-based systems.

WICK SYSTEMS (PASSIVE)

This is probably the simplest media-based system and a good one for exploring capillary action. A nutrient mix is drawn into the medium through nylon or cotton wicks immersed in a reservoir. This is commonly used in schools where the biggest challenge is making sure the plant roots get sufficient air and that the nutrient mix is diluted with water when the level drops.

EBB AND FLOW SYSTEMS (ACTIVE)

The plants and medium are flooded up to six times per day with the nutrient mix, then allowed to drain. As it drains, the system draws oxygen into the medium. These systems often incorporate automatic timers, but can be flooded by hand if you are very consistent. After several cycles, you must wash the roots and tank to remove any built-up, crusted salts.

TOP-FEED OR DRIP SYSTEMS (ACTIVE)

A timer-controlled pump delivers the nutrient mix on a regular schedule through "emitters" (pipes with holes) to the top of the plant medium and allows the mix to drip down into a catch basin below.

Water-Culture Systems

These systems do not use any medium other than water, so they require a support material such as wire mesh to keep the plants from drowning. These systems rely on regular contact between plant roots and the nutrient solution. Leafy crops like lettuce and herbs tend to do better in water culture than do fruiting crops like tomatoes, cucumbers, or peppers.

RAFT SYSTEM (ACTIVE OR PASSIVE)

In this system, plants float on rafts above a reservoir of nutrient solution. (Styrofoam rafts work well in the classroom.) The tips of the roots reach the liquid and the holes cut in the raft for the plants allow some air exchange. Many raft systems also aerate the water automatically, to provide the roots with greater exposure to oxygen.

NFT (NUTRIENT FLOW TECHNIQUE) (ACTIVE)

Plants are suspended in the nutrient mix, which is pump-circulated past the roots, aerating the solution. Commercial growers often place seedlings directly into rockwool cubes within holes cut in PVC pipe channels.

AEROPONICS SYSTEMS (ACTIVE)

At regular intervals, plants suspended in the air are sprayed or misted with the nutrient solution. This technique, dependent on high-tech growing methods, is the one used by Disney's Epcot Center.

Simply Super School Setups

CREATING HYDROPONIC UNITS FROM AVAILABLE MATERIALS

Garden in the classroom with hydroponicsYou and your students may want to experiment with your own designs, or try some that other classrooms have used successfully. The following systems have been used by classrooms in our growing network. We encourage you and your students to try them out or create a variation, then share your experiences with us and other budding hydroponics growers. For more detail on the design and use of other school setups (such as the one depicted, left), go the the Classroom Storiessection of this guide.
Click on the name of the setup for directions on how to make and use it.


Basic Wick

The Wick System is probably the simplest media-based system

GROWING TIPS


1.   Place one end of the wick an inch or two into the container so it contacts the plant roots, then thread the wick down through the drainage hole into another container holding nutrient solution.
2.   Fill the top container with the growing medium.
3.   Keep the nutrient solution level constant by adding water as it evaporates and is transpired, and change the solution every week or two. Try to keep the nutrient solution pH between 5.8 and 6.5 and the temperature at about 70 degrees F.


Milk Carton & Rockwool

GROWING TIPS


1.   Plant seeds 1/4 inch deep in rockwool that has been soaked in a dilute nutrient solution and cut to fit in the milk carton. Place rockwool in a tray of water until seeds germinate.
2.   Try to keep the nutrient solution pH between 5.8 and 6.5 and the temperature at about 70 degrees F.
3.   Once seeds have sprouted, move the rockwool with the plant to an empty carton every day, pouring new solution over the rockwool into the new carton.


Soda Bottle Aeration

Growing Tips

1.   Cut the top from one soda bottle, then remove the black base from another bottle. (Do this by filling the bottle with hot water to soften the glue, then prying the base loose.)
2.   Invert the base and cut a hole in it for your seedling or cutting, and another one to insert aquarium tubing.
3.   Insert aquarium tubing through the hole and connect the other end to your pump.
4.   Gently insert a seedling or cutting through the center hole in the inverted base and wrap aluminum foil, dark plastic, or paper around the setup to exclude light from the roots and discourage algae growth.
5.   Try to keep the nutrient solution pH between 5.8 and 6.5 and the temperature at about 70 degrees F, and change it every two weeks or so. Some people suggest using a half-strength solution for the first week.

Floating Styrofoam Raft

GROWING TIPS


1.   Soak rockwool cubes with a dilute nutrient solution and place a seed in the top of each cube.
2.   Cut a styrofoam raft to fit in the container, then cut holes in the raft, spaced 6 to 9 inches apart, to snugly fit the rockwool cubes. Be sure the cubes extend to the bottom of the raft.
3.   Poke the aquarium tubing through the raft into the solution. Keep the aquarium pump outside.
4.   Fill the container with water around 70 degrees F to within 1 inch of the top, then float the raft with planted cubes on the surface.
5.   When seedlings appear, add nutrients to the water at half the recommended strength. Try to keep the pH between 5.8 and 6.5. Let the air pump run continuously. After a week, raise the nutrient solution to full strength and maintain a constant level. Change the entire solution every 2 weeks.




Basic Ebb and Flow

GROWING TIPS


1.   Soak rockwool cubes in dilute nutrient solution before planting seeds 1/4 inch deep. Place cubes in a tray of water until seeds germinate.
2.   Protect the drain outlet in the planting bucket from clogging by placing some crushed rock around it.
3.   Place cubes with seedlings in the moistened growing medium. Then put the bucket of nutrients into the fill position and allow the medium to fill to approximately 1 inch below the surface.
4.   Allow the solution to remain for about 20 minutes, then put the bucket in the drain position. Repeat this three to six times per day.
5.   Always keep a lid on the nutrient bucket. Try to keep the nutrient solution pH between 5.8 and 6.5 and the temperature at about 70 degrees F, and change the entire solution every two weeks.


Simple Straw Aeration

Growing Tips

1.   Use a utility knife to carefully cut a 1-inch X shape in the center of the lid.
2.   Cut a smaller X shape in the lid, about 1 inch from the edge, large enough to insert a drinking straw.
3.   Carefully clean the roots of a 4- to 6-inch-tall seedling (cucumber, lettuce, herb, etc.), washing off the perlite or other medium used to start it.
4.   Gently insert the seedling's roots through the large X, then insert some cotton balls between the stem and the hole to protect and secure the plant.
5.   Fill the container with a dilute nutrient solution, then secure the lid. Make sure that the root system, but not the stem, is completely immersed.
6.   Insert a drinking straw through the smaller hole into the solution. Twice a day, gently aerate the solution by blowing into the straw.
7.   Try to keep the nutrient solution pH between 5.8 and 6.5 and the temperature at about 70 degrees F. Change the nutrient solution every 2 weeks, using a full-strength mix.


Plexiglass Slants

GROWING TIPS


1.   Drill holes about 2 inches apart on either side of plastic container to accommodate dowels.
2.   Cut Plexiglass with a utility knife to fit in container, as illustrated (or have it cut at hardware store).
3.   Wash fabric interfacing (to remove the flame retardant which is toxic to plants), then cut it the same size as your Plexiglass slants.
4.   Make a "sandwich" to lean against each dowel by placing a moistened square of interfacing between two pieces of Plexiglass. Wrap the sandwich side to side with black plastic to prevent light from reaching roots.
5.   Use clothespins to hold the sandwich together and to help maintain it at about a 45-degree angle in the container to maximize absorption of the solution.
6.   Start seeds (lettuce, alfalfa, beans, etc.) by placing them between the interfacing and the Plexiglass, about 1/4 inch below the top edge. (You can also start seeds in moist perlite, then gently clean the roots and transplant them to the slants.)
7.   Fill the container with 2 inches of nutrient solution with a pH between 5.8 and 6.5. Keep the level of the solution constant, and replace it with fresh solution every 2 weeks.
8.   You may want to cover the open solution with black plastic to reduce light and keep down algal growth. If you do have a lot of algae, remove slants and clean out the container with a dilute bleach solution before putting in your next batch of nutrients.


Curriculum Connections

Your school's hyroponic system can vary in size, design, and materials used.SPARKING SCIENCE INQUIRY, MEETING STANDARDS

This section offers some ideas for planning hydroponics experiences to help students explore key concepts and generate their own investigations. How you begin to study hydroponic gardening with your students depends on your own philosophy, your curriculum objectives, and the developmental levels of your students. You may wish to have one large hydroponics setup in your classroom to which each child contributes ideas and materials. Or you may ask small groups or individuals to choose a design or invent their own setup based on their understanding of plant needs and hydroponics.
Hydroponics projects can support these different learning styles and provide an opportunity for students to appreciate one another's differences. Consider establishing small cooperative groups of two to four students, while still allowing students to work alone for short periods of time. Make reference materials available in your classroom or in the school library. Create a climate in which students share their discoveries with the class. Invite final reports and creative presentations. Challenge students to pursue their own questions and establish a knowledge base through active investigation.

School hydroponic gardeners making discoveriesCULTIVATING INQUIRERS

As students work with hydroponics setups and concepts, their experiences and observations are likely to spark a variety of questions they can actively investigate through observations, experiments, or additional research.
·      How do plants grown in a soil-based (geoponic) system differ from those grown in a hydroponic system?
·      What might happen if we leave out a specific plant nutrient, or put in too much of another?
·      Can we use houseplant fertilizers for hydroponic growing?
·      How does the growth of plants grown with different amounts of aeration compare?
·      Can we invent an automatic hydroponic unit from recycled materials?
·      Can we grow enough herbs to share or sell?
·      Can we simulate a pond or other wetland environment using what we know about hydroponics?
As students conduct and begin to make meaning from their investigations, it's important to help them reflect on their experimental setups. Encourage them to review and critique their own and others' science process by asking questions, in journals and in group discussions or reviews: Was this a fair test? What other variables besides those we tested could have influenced our results? How could we revise this experiment if we were to do it again?
Consider ways to help students make connections between their classroom experiences and broader concepts and issues in science and technology (raising food in space, for instance). Communicating with others can help them make these connections. For example, they might write a series of directions or produce visual or dramatic displays to demonstrate their understanding of an aspect of hydroponics. Involving a real audience such as parents and other community members can serve as a powerful learning tool, good public relations, and a way for you to assess what your students have learned. Hydroponics units may spark an interest in learning more about the real-life and potential applications of hydroponic technology, as well as its limitations. Keep an eye on local supermarkets for hydroponically grown vegetables, and look for hydroponic facilities to visit at commercial or public greenhouses and nurseries. The Classroom Stories in this guide reveal how other classrooms have branched out with hydroponics.

ADDRESSING SCIENCE STANDARDS

As with any unit, it's important to identify what you hope students will gain from the activities and investigations, recognizing that a range of unintended outcomes will also emerge as students explore based on their own interests. Following are just a few of the National Science Education Standards-related concepts and skills that you might address in a hydroponics unit.
·      characteristics of organisms (needs and environments that meet them)
·      life cycles
·      structure and function in living systems
·      asking questions about objects, organisms, and events
·      planning and conducting investigations (and fair tests)
·      seeking information from reliable sources
·      working individually and in teams to collect data and share information and ideas
·      identifying problems, proposing and implementing solutions
·      designing technology
·      understanding science and technology


Mini-Lesson Stations

EXPLORING THE BASICS

Before setting up a complete hydroponics system, you may want to involve students in some short hands-on activities to explore some of the key factors affecting hydroponic setups. This section offers some ideas for "stations" that could be set up as learning centers before or during your hydroponics study. The stations are in no particular order and can be modified easily to suit your students' abilities, interests, and prior knowledge.

STATION 1: SUPER SOUP: MIXING THE NUTRIENT SOLUTION

Purpose: To learn correct procedures for combining the materials for a hydroponic nutrient solution
Materials: Nutrients, in the form of commercial powdered or liquid hydroponic mixtures or as individual mineral salts, water, containers, measuring equipment, stirring rods
Procedure: Have students follow container directions or a recipe for mixing nutrients, being careful to measure exactly.
Challenge Questions: What are nutrients? Which of these might you investigate in the classroom? What do you think might happen if you use a stronger nutrient solution than called for? A weaker solution? How might you design your own "secret formula" to grow plants? How would you measure your success?

STATION 2: PH: THE ACID TEST

Purpose: To learn how to measure and change pH in a liquid
Materials: pH paper or test kit, vinegar, baking soda, containers, distilled water
Procedure:
·      Teach students how to find pH. Provide about 100 mL of distilled water per container. Dip a pH paper strip into the liquid being tested and compare the color change to the chart provided with the paper, or follow directions on your pH test kit.
·      Next, challenge students to change the pH in some prescribed way (e.g., lower pH to 6 or raise it to 7), keeping track of the number of drops or pinches of baking soda needed. (The solution will fizz when vinegar and baking soda mix, much to students' delight.) Ask students to test and experiment with the pH of the different nutrient mixtures.
·      You may want to precede this activity by encouraging students to brainstorm, then gather common solutions to test (e.g., orange juice, shampoo, household cleaners) to give them a better foundation for understanding the range of pH numbers.
Challenge Questions: How might a very acidic solution affect your hydroponically grown plants? A solution with a higher pH? How could you set up an investigation to find the answers to these questions? In what other situations might you need to know the pH of a solution? How else might scientists use pH?

STATION 3: PLANT PERSPIRATION

Purpose: To discover that water can be lost from leaves through transpiration in a hydroponic setup, how to compensate for that loss, and explore the purpose of transpiration
Materials: Samples of different leaves with stems, graduated cylinders (one more than you have leaf types), modeling clay, water
Procedure: This investigation takes about 2 days.
·      Fill each graduated cylinder to the same level, and mark the water line.
·      Wrap the clay around each leaf stem and insert the leaf and clay into the mouth of the graduated cylinder. Make sure that the leaf stem is well below the water level and that there is no air space between the stem and the clay or between the clay and the cylinder. As a control, simply plug one cylinder without a leaf.
·      Place all graduated cylinders in a sunny windowsill and observe the level of the water in each over the 2 days. Water will move up the stem of the leaf and out through small pores in the leaves (called stomates). Students will see varying amounts of water loss from the cylinders.
Challenge Questions: What does this investigation indicate about leaves and water? How does transpiration affect the air plants use? Why did we have a plain cylinder with no leaf in it? (This served as a control, to show that all water loss was actually through the stem and leaf). What do your observations tell you about what might happen in a hydroponic system that you set up? How might you deal with replacing the moisture lost through transpiration?

STATION 4: A MEDIUM WELL-DONE

Purpose: To investigate different kinds of media for their water-retaining properties
Materials: A variety of potential hydroponic media (e.g., sand, perlite, cloth, rockwool, aggregate), magnifying glasses, water, containers, waxed paper or recycled foam trays for a work surface
Procedure:
·      Provide or ask the students to bring in a range of materials other than soil that they think might support plant growth.
·      Have them examine the various media with hand lenses, making observations and sketches of the different structures.
·      Ask students to predict which might absorb the most water, then choose one to try using in a simple hydroponic system.
Challenge Questions: Can you explain why you chose what you did? Can you invent ways to compare the water-absorbing properties of each medium? If you could design the perfect hydroponic medium, what would it be like?

STATION 5: LET THERE BE NO LIGHT

Purpose: To observe the effect of light on plant root development
Materials: Two identical clean glass jars, water-absorbent polymer crystals, two similar ivy cuttings, black plastic or other dark material sufficient to wrap one of the jars
Procedure: This will take about three weeks.
·      Add 1 to 2 teaspoons of polymer crystals to each jar and fill it with water. (The crystals turn jelly-like when wet.)
·      After the crystals have swelled to fill each jar, gently poke a piece of ivy into each.
·      Cover one jar with black material and leave the other uncovered. Place both jars on a window and observe. (Students should note that the roots in the covered jar form more strongly and fully. This is because light is actually a deterrent to active root growth.)
Challenge Questions: How do the roots in the two jars compare? Why do you think roots formed the way they did? How might the results of this investigation influence the


Floating Gardens and Soda Bottles

SIXTH GRADERS BUILD BETTER BOTTLES

"After exploring soil and basic chemistry with my sixth grade team, we talk about plant needs," reports Los Angeles, CA, teacher W. Alden Wright. Even in this urban school, it's common knowledge that plants and soil go hand in hand. "So when I tell the students that, well, we're not going to use dirt, they are absolutely disbelieving," explains Alden. Water power, he tells them, will be the name of their game.

FLOATING FARMS

Alden launched his hydroponics unit with a bit of history, teaching students that the Aztecs designed some of the earliest hydroponics systems out of necessity. "In an effort to protect their food from enemies, they built mud-covered floating rafts for growing crops," says Alden. Determined to create models of these floating farms, student groups loosely lashed twigs together to form mini-rafts, topped them with soil, water, and grass seed, then floated them in "ponds" made from plastic trays or lined cardboard boxes.

SIMPLE SODA BOTTLE SYSTEMS

Once their raft gardens sprouted, students prepared to create individual hydroponic setups by gathering clear 2-liter soda bottles, then selecting seeds to grow. (Despite contrary wisdom that light inhibits root growth, the Alden has discovered that plants actually grew better in clear bottles than in colored ones.) "I told students they could choose any two salad vegetables," says Alden. Lettuce, anaheim chiles, cherry tomatoes, nasturtiums, and basil were among the selections. Each student started 4 seeds in each of two 1- by 1-inch cubes of rockwool. "As the seedlings grew, I had students cull all but one in each cube, and required them to justify their choices," says Alden. When seedlings were a few inches tall, students transplanted them to their soda bottle setups.
"My team teacher (who is also my wife) and I spent a day with our 60 students building the planters," says Alden. "Our objective is to keep it simple. Our cost is just 9  cents per unit." Here are the nuts and bolts of their setups: After cutting off the top 1/3 to 1/2 of the bottle, drill a 1/4-inchhole in the cap. Meanwhile, cut a 1- by 10-inch strip of dress interfacing, which will draw the water/nutrient solution up from the bottom reservoir to the plant roots. Next, invert the top section and set it in the bottom half. Feed the wick up from the bottom reservoir, through the bottle cap, and into the inverted top. Fill in around the wick in the top with perlite. When the seedling in rockwool is ready to be moved to the setup, continue the wick in an "s" shape into the bottom of the rockwool, then fill around and just above the cube with perlite.
"I usually work in a chemistry lesson by having students build their own fertilizer from a variety of minerals and we sometimes experiment with ratios," says Alden. "It's amazing how quickly you can see results in hydroponic systems." That done, I then tell them that we can simply use Schultz plant food." Students are responsible for deciding when to change the nutrient solution, or when to simply add more water and nutrients to what's there. When they change the solution, many try a low-tech effort to provide oxygen to plant roots: blowing bubbles through a straw!
"We've had great luck raising most salad vegetables in these setups under fluorescent lights, except for celery and carrots," says Alden. In fact, the class had cherry tomatoes that climbed up the wall all the way to the ceiling on netting. As the plants grew and bore fruit, students keep daily growth logs on plants, which also include drawings. "One student had drawn his pictures in the same corner of each page in his journal, and has he flipped through the pages one day, discovered that his plant seemed to grow!"
"Food is such a puzzle for these urban kids," says Alden. "You know, the chocolate milk from the brown cow sort of thing. But kids get so excited about caring for from something from seed to stomach and knowing they can grow their own food; and they do take the concepts home with them." One student, he explains, even made a hydroponics setup for his apartment bedroom window. "As long as it's fun for me, I'm sure it will be fun for them," he says. "And I love how much we learn from the kids."


Soilless High School Greenhouse

BIOLOGY AND BUSINESS SKILLS COME TO LIFE

Peoria, Arizona has a long history of growing food hydroponically. Commercial growers in this west-central region have used sand-based hydroponics to grow tomatoes for over twenty-five years. High school teacher, John Mulcahy, bridges the past and present by using hydroponics in his science curriculum at Peoria High School. John teaches Specialized Horticulture to students in grades 9 through 12 enrolled in the school's Agricultural Program. His students learn the biological components of growing plants and the business aspects of producing, promoting, and delivering their products to market. There is strong support, within the school and community, for teaching students both the historical aspects and the horticultural importance of growing plants hydroponically.
"This is our fourth year working with hydroponics in the greenhouse. We model our production process on the "EuroFresh" method that is used in our area. This way, our students have relevant experience for future job opportunities," John explains. "We integrate the studies of horticulture, greenhouse growing, and hydroponics with other disciplines."
John's horticulture students also work with the Biology Program to study pest management and the Culinary Arts Program which uses the hydroponically grown fruits and vegetables in the school's lunch menus and for special events.

FROM AERATING TO ADVERTISING

The students participate in every aspect of hydroponics -- from designing hydroponic systems to marketing their produce. When the hydroponics curriculum first began, John's classes used the NFT system for growing. "The NFT system is extremely easy to use and has lots of room for trial and error," notes John. "We still use it for growing lettuce, cilantro, and basil. But my students wanted to get into tomato production and we needed more structural support for this type of plant. After much research, we agreed to go with the horizontal bag system."
Students also participate in marketing strategy meetings to develop a plan of action for public relations, sale events, and crop selection. Once a month the students hold plant and produce sales for the general public and sell their goods to the employees of the school district on a regular basis. The proceeds go back into the program's budget to buy equipment and advertising materials.
The bag system uses a growing medium such as perlite. The plants are planted into the bag and liquid nutrients are circulated through the growing medium. Plants are supported from above with piping and string.Students also volunteer for year-long responsibilities in the greenhouse hydroponics setup. Different students manage the greenhouse hydroponics, check growing systems, regulate nutrients, and harvest produce. This year, the students decided to set a goal of growing one ton of tomatoes hydroponically. They chose a vertical aeroponic system and then custom-designed the hydroponic units with parts donated from local suppliers. The project has brought biology -- as well as plants -- to life. "With hydroponics, the kids get to see an immediate reaction to a cause," John explains. "The balance of nutrients, pH, and other environmental factors has a direct and visible effect on the plants. I've heard my students say "wow it really does make a difference' after they've experimented with different levels of nitrogen or phosphorous in the nutrient mix."

TANGIBLE RESULTS

"The kids know that once you start a hydroponics system, you have to manage it, you've got to put your time in," says John. "The kids do it all, they're capable, in charge, and they do the actual work. They're successful through their own efforts."
John believes that incorporating hydroponics into his studies has helped fulfill his educational mission: provide students with information, give them a problem to solve, and let them reach their own conclusion. Through the program's hydroponic tomato growing enterprise, his students have learned many lessons: botany, biology, marketing, managing budgets, retail sales skills, and that they do have a future of their own choosing. "One year, the student tomato manager was a kid headed to nowhere," Mulcahy remembers. "His sophomore year he started working with the hydroponics program and it really turned him around. He became excited, interested, and he saw that his actions really made a difference. Now he's off to college studying horticulture with a special emphasis on hydroponics. He told me he's going to be 'the top producer of tomatoes in the world'."









Kindergartners Coddle Cukes

UNDERSTANDING GROWS IN URBAN CLASSROOM

Although hydroponic growing may seem to require technical savvy appropriate for older students, Chuck Lafferty's kindergarten students in Philadelphia, PA, were nonplused. "I like to use life science as a theme for all we do," says Chuck. "Since our inner city school has little room for an outdoor garden, I purchased a Hydrofarm hydroponics unit two years ago so we could raise food plants, through their life cycles, in the classroom."
From arrival of the hydroponics unit to final harvest, says Chuck, his first group of soilless farmers were thoroughly engaged in maintaining the operation. Together they assembled the unit and then chose vegetables and flowers to try growing. "We had to begin by discussing where our food come from, and then tried to imagine what different food plants might look like," says Chuck. From November through March, the kindergarten scientists maintained nutrients and pH, observed, measured, kept journals, and even played the pollinators in their soilless garden. The cucumber plants were perhaps the biggest success, explains Chuck. When the flowers emerged, he had the kids buzz about dabbing the blossoms with an eye toward spreading pollen. The upshot? A classroom party to celebrate (and eat) their 12-inch-long cukes.
"Earlier that fall, we had harvested seeds from giant sunflowers we grew outdoors," says Chuck. The class took a stab at sowing the seeds in the hydroponics setup and the room eventually sported an enormous green sunflower stalk, but never yielded a flower. "Next year we might just try a dwarf variety," he says wryly.
When Chuck received a Youth Garden Grant from the National Gardening Association, his students were able to apply much of what they'd learned from their hydroponics project to a new context. "The kids already knew how to care for plants and understood much more than they had about how plants work," explains Chuck. Applying their understanding of plant life cycles, Chuck and his students created a little business venture from their harvest: The Kindergarten Seed Company. The kids gathered selected garden seeds and counted out batches of five to put in re-sealable plastic bags. Each student then created a label for a particular seed packet. "The plant labels were actually good assessment tools," says Chuck. "Students' drawings became much more detailed - from lollipop figures to details of roots and leaves - once they'd seen plant life cycles up close in the classroom and garden." These gains, it seems, may also have been reflected in standardized science test scores where, Chuck reports, students who went through these growing experiences soared. "I think that caring for and watching their plants grow has also had a wonderful calming effect on the students and has increased their respect for nature and for each other."