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
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?
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
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.
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
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.
·
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
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
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
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
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
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
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?
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
·
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
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
Finding Volunteers
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
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?!
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
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!
ROOTS AND SHOOTS
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.
Nutritionally Speaking
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
Mixed Media
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
A Breath of Fresh Air: Getting Oxygen to the Roots in the
Garden
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
ARTIFICIAL LIGHT
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
·
lettuce
·
beans
·
houseplants
·
annual flowers such as marigolds, zinnias,
nasturtiums
·
tomatoes
·
cucumbers
·
bell peppers
·
corn (in tubes)
GROWING FROM SEED
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
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
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.
"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!"
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.
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.
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."
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