School Greenhouse Design Tips

Orientation
Faculty must research the proper orientation and equipping of the greenhouse. In the northern hemisphere, the best orientation is due south;

A high school lean-to greenhouse

however, southeast and southwest orientations can also be acceptable. Greenhouses are usually constructed of glass or translucent extruded cellular polycarbonate and, therefore, allow a lot of daylight inside. This may be great for some school uses but too much light for others-many plants are sensitive to direct, intense sun that can burn leaves or cause plants to dry out quickly-which leads to the need to provide some form of shading.

Commercial greenhouses provide shading by means of shades of aluminum slats or mesh or ultraviolet- resistant fabric, which roll up and down on the outside of the structure like ordinary window shades. More elaborate and expensive options include motorized shades that can respond automatically to the amount of sunlight on a given day.

Ventilation
Proper ventilation is crucial because without it the greenhouse can rapidly become unacceptably hot. Most greenhouses have vent panels in the roof and near the ground that can be manually opened and closed to allow fresh air in to mitigate heat buildup; the primary drawback to a manual operation is the chance that the person responsible will forget to close the vents at night or on a cold day, or forget to open them the next morning. (For instance, I have lost plants in my greenhouse because I forgot to close the vent.) For a price, the vents can be automated and thermostatically controlled to open and close depending on the inside temperature of the greenhouse. An automatic ventilating fan system should also be considered with the fan at one end and an automated louver at the other, both controlled by a thermostat to bring in fresh air as needed.

Cooling and heating
Evaporative cooling-the mechanical equivalent of the old cartoon of a person setting up a fan to blow across a block of ice-is a relatively

A large evaporative cooler panel

inexpensive way of cooling a greenhouse while at the same time increasing the humidity level. Such a “swamp cooler” should be controlled by a thermostat.

In most climates in the United States, heating the greenhouse is also a necessity. While the space can rapidly heat up during a sunny day, it can quickly become cold enough to allow plants to freeze at night or even during the day when the weather outside is frosty. Small gas furnaces can serve the greenhouse space itself or the building heating system can be extended into the greenhouse. In a St. Louis area school renovation, where a small lean-to greenhouse was installed on the roof of a heated space, the school’s steam heating line was extended up through the floor and a small radiator with a thermostatically controlled steam valve kept the greenhouse warm on cold days. Faculty could also consider using solar heat reradiated from a Trombe wall-a massive wall facing the sun that absorbs the sun’s heat during the day and reradiates it at night-as an energy-saving source that can be supplemented by a more traditional heat source.

Water supply and drainage
Another necessity, probably a no-brainer but occasionally overlooked, is water supply. Plants do generally need to be watered either manually or by an automated system. My small greenhouse includes a laundry sink with both hot and cold water and a threaded faucet to which I attach a hose and watering wand. Larger greenhouses should probably have one or two hose bibbs centrally located to allow the connection of a hydroponic watering system or simply a hose. Also, when watering plants, the overflow needs someplace to go, which requires one or more floor drains. The floor of the greenhouse should be constructed to slope toward these drains.

Lighting
Lighting should also be provided. Waterproof fixtures should be chosen, probably with fluorescent lamps; how the greenhouse will be used should determine how it is lit. Are grow lights needed to supplement the daylight? If the greenhouse is also an architectural amenity, should it be lit at night? Faculty should also consider the need for electrical receptacles within the greenhouse. Both the lights and the receptacles should be on ground-fault protected (GFI) circuits.

Materials of construction and furnishings
The floor in a greenhouse should probably be bare, sealed concrete. Rubber mats can be placed in walkways between plant benches, allowing water to flow along the floor while minimizing the chance for a person to slip and fall.

Structural plastic plant tables

Plant benches should be either aluminum or structural plastic that is resistant to ultraviolet radiation. Freestanding plant benches will allow flexibility in arrangement as well as in periodic cleanup. A table or counter should be provided as a potting bench and tall cabinets for storage of materials and supplies. Such casework should not be made of wood or plastic-laminate-covered particleboard as these materials will rapidly deteriorate in a moist environment. A door directly to the outdoors can often be helpful, particularly if the greenhouse is adjacent to an outdoor garden space.

Location
Finally, faculty should make sure that the resulting greenhouse design works as a greenhouse-it is used and cared for, and not just a visual, remote addition to school grounds. Location is important. When properly planned and designed, a good working greenhouse or plant window can be both a science teaching resource as well as a wonderful architectural amenity.

This article originally appeared in the November 1, 2006 edition of The Science Teacher.