Article #4

Small Greenhouse

A small greenhouse is most commonly used to grow starts from seeds before the weather is warm enough to safely plant the seeds out of doors. Tomatoes are a favorite crop to start in this way, but any plants requiring a longer growing season than your area provides can be started in a greenhouse.

A greenhouse relies on the "greenhouse effect" (which, on a larger scale, keeps the Earth warm enough for life to survive) to maintain warmer temperatures than prevail outside. The glass or plastic of the greenhouse is transparent to visible light but opaque to infrared radiation. Thus, sunlight penetrates it on the way in, but much of it is trapped on the way out after being reflected at a longer wavelength.
 

Small Greenhouse Plans

A small greenhouse is easy and cheap to build for oneself. The materials required include something for a frame, usually wood, aluminum, or galvanized steel, of which wood is the easiest to work with. Plastic pipe is not recommended for a greenhouse frame because it is not strong enough to stand up to wind or bear a load of snow in many locations.

The covering material can be glass, fiberglass, rigid plastic panels, or plastic film, of which the first is the most expensive to construct initially but (as long as it remains unbroken) the cheapest to maintain and the most durable, with the other materials declining in both price and durability.

For a small greenhouse, greenhouse plastic film is probably the most common material. It can be bought cheaply in grades that will last three to four years and is easy to work with. Tools required depend on the materials. For a wood-frame greenhouse with plastic-film covering, you will need a saw, hammer and nails or screwdriver and wood screws, and perhaps a heavy-duty staple gun and staples.
 

Small Greenhouse Heater

Although a small greenhouse maintains a higher temperature than its surroundings just through the greenhouse effect, in particularly cold climates or when raising particularly cold-sensitive plants it may be necessary to provide artificial heat as well. There are essentially two ways to do this. One way is to build the greenhouse as an attachment to your home or other heated building and vent the warm air from the building into the greenhouse. The other way is to provide a separate heater and electric connection for the greenhouse.

If you need to provide a heater for your small greenhouse, it's likely that ordinary space heaters will work fine. Gardening supply houses offer heaters specifically designed for greenhouses, including gas, electric, and steam-based heaters, but these are often more expensive and for a small greenhouse one or more electric space heaters is completely adequate. A good rule of thumb is to provide 77 BTUs of heat per square foot of greenhouse space in very cold climates. A single 1,500-watt electric space heater puts out 5,115 BTUs, so one of these would be more than adequate for a greenhouse up to about 70 square feet.
 

Small Greenhouse Humidifier

In most cases there will be no need to add humidity to the air of your greenhouse, as the respiration of plants naturally adds humidity. However, if you live in particularly dry climates, or if you are using your greenhouse to raise plants with high humidity requirements such as orchids, you may need to do this. For a small greenhouse, you can simply use a bucket or several dishes of water, left in the greenhouse to evaporate and add moisture. Commercial humidifiers are available, but unless you need very precise humidity control for some reason, you should not need to buy one.