The first thing to address is whether a greenhouse is justified? Across the nation there is an increasing need to prepare students for the many careers related to the horticulture and the plant sciences fields. Horticulture science is considered one of the fastest growing segments of the agriculture industry, while plant biotechnology and genetic engineering are also booming. Students that gain experiences through greenhouse activities have a distinct advantage over those who do not when it comes to preparation for career in those fields.

It is important that people whose business is greenhouse construction are involved in new greenhouse construction projects. Those people have an understanding of the unique requirements involved in growing plants under glass. If the school district is building a new building or an addition that includes a greenhouse, prepare a separate contract with a greenhouse builder to design and build the greenhouse. Although this requires more effort, it will ensure the construction of a functional greenhouse structure.

The following addresses specifications to consider when planning a greenhouse.

Size

The size of the structure obviously is dependent on the anticipated use and the number of students involved in instruction. A minimum of 60 square feet of greenhouse area per student, with 30 square feet bench area per student should be provided (i.e. minimums for class of 25: 1,500 sq. ft. greenhouse space and 750 sq. ft. bench space).

A headhouse in which supplies can be stored and plants potted should be attached to the greenhouse growing space. A minimum of 600 square feet should be available for this purpose. Typically, a headhouse will have a partition between it and the greenhouse growing space.

Location

The location of the greenhouse facility is very important. Ideally, it should have an east-west orientation on the south side of the school. This orientation allows the greatest light transmission for plant growth.

It should also be accessible through a door connecting it with the agriscience/horticulture classroom. Plants need frequent care and should be checked for water and temperature needs a minimum of 2-3 times a day. Regular visits are made easy when the greenhouse is attached to the classroom. This is particularly important during inclement weather.

School security lights, parking lot lights, football field lights, and car lights can disrupt the timing of crops. Keep this in mind when locating the house. It may be necessary to protect the greenhouse crops from those sources of light.

Structure

Build the best possible structure that can be afforded because it is seldom that a facility is upgraded once it is installed.

A. Begin with an aluminum framework or an aluminum and steel combination framework. Though somewhat costly, they are long lasting and maintenance-free. Install a greenhouse that is high at the gutters to allow for the installation of energy curtains.
B. Pour a solid concrete floor with plenty of drains. Concrete may be expensive, but it is very easy to keep clean of weeds and growing medium. Concrete floors also permit greater mobility for physically disadvantaged students.
C. Cover the house with polycarbonate structured sheets treated to resist ultraviolet wavelengths or tempered glass.

1. Polycarbonate has a number of advantages:
a. It is much stronger than glass, but lighter in weight.
b. It has good insulation properties.
c. It has excellent light transmission.
d. It is flame retardant.
2. Tempered glass also has merits.
a. It provides excellent light transmission for plant
growth.
b. It is long lasting.
c. Tempered glass is stronger than regular glass.
d. However tempered glass may still break during
hailstorms and it has a high initial cost.
3. Other common glazing materials are generally less
suitable for school greenhouses:
a. Fiberglass loses light transmission as it wears
out and it becomes extremely flammable as it ages
and fibers become exposed.
b. Polyethylene is the least expensive covering
material, but it tears and must be replaced every
1-3 years depending on the thickness of the poly used.
c. Acrylic has good light transmission, but it is brittle.
4. A number of materials are effectively used for benching.
Extruded metal is commonly used. It provides good air
circulation and allows water to drain from pots. Plastic is also
becoming more widely used. Keep benches narrow enough
for students to reach for and care for plants. They should
not have to reach more that 30", so limit the width of benches
with access from two sides to 5 feet.
5. Leave wider aisles than would be found in a commercial
greenhouse to accommodate class size groups and students
with special needs.

Climate Control

Perhaps the most important greenhouse consideration is the ability to control the temperature at all times (weekends and holidays included).

1. An automatic temperature control system, preferably
computerized, should be included.
2. Heating of the house should be done by unit gas heaters.
Never tie the greenhouse heat to the school boiler room.
3. Cooling is a must, and the best method of cooling involves
a fan and pad system. A greenhouse can get much too hot for
plants, even in April, May, June, September and October when
school is in session.
4. Ventilation alone can cool a house during many times of
the year. Ventilation can be accomplished with vents and an
air-jet system.
5. Consider installing energy curtains that reduce heat loss
at night during cold periods and keep plants cooler in the day
during warm periods. Modern commercial greenhouses use
energy curtains extensively.
6. It is often useful to divide the greenhouse with a wall and
to separate environmental controls so that one room can be
kept at less than 60 degrees at night and the other above 60
degrees at night. This allows the students to work with plants
requiring different conditions.

Headhouse

The headhouse should have:
1. 16-20 feet of potting bench space.
2. An outside entry large enough for supplies and
wheelbarrows. (An overhead door should be considered if
there is a need for vehicle traffic.)
3. Storage space for growing media and pots.
4. Separate temperature control from the greenhouse.
5. A custodial sink.

* Translucent polycarbonate sheets make a good glazing material for the headhouse.

Utilities

1. The greenhouse and headhouse should have waterproof
electrical outlets for pumps, lights, timers and other items
that may be used with laboratory exercises. Also, enough
water faucets should be installed so hoses can easily reach
all benches and so 50' hose fulfill the need.
2. It is also recommended that a large capacity water heater
be installed to reduce the shock to plants created by cold
water. Research has shown that use of cold water significantly
slows growth and development.
3. Associated with the water system, it is recommended to
install a fertilizer injector system with the greenhouse
plumbing. Controls should be installed with the injector system
that allows it to be switched on or off.

Chemical Storage

With a greenhouse and the growing of plants comes the need to use pesticides and growth regulators. An appropriate, locked storage cabinet, vented to the outside should be installed in the headhouse to store chemicals.

Security

If security is a concern, consider a cyclone fence encompassing the greenhouse to keep vandals away. Security lighting may also be beneficial as long as the light itself doesn’t shine on the greenhouse causing photoperiodic problems with the greenhouse crops. Fixtures with a shield should be selected and installed in a manner that will direct all light away from the greenhouse.

PARTIAL LISTING OF GREENHOUSE
BUILDERS AND DESIGNERS