Among the earliest greenhouses, compost was one of the methods that growers used for reliable heat. Early gardeners from Roman times through the French in the 17th century heated artificial growing rooms with rotted manure. These early gardeners noticed that as organic materials decompose, they release heat that has a warming effect on nearby plants. Take advantage of this today by composting organic materials such as wood chips in your greenhouse.
Construct compost bins throughout your greenhouse by stacking hay bales to create troughs with abutting corners. The interior of each trough should be at least three cubic feet.
Collect compost material and separate it into organic green and organic brown material. Organic green material is fresh, filed with nitrogen and sometimes green in color. Examples include manure, peat moss, kitchen scraps, grass clippings and clover. Organic brown material is usually dead, filled with carbon and often brown in color. Examples include wood chips, sawdust, dead leaves and straw.
Chop the compost material into one-inch-long pieces to make them decompose faster (and help your compost pile get warmer). Use a lawn mower for the dry material such as grass clippings and straw. Use kitchen shears for the kitchen scraps.
Pile your organic green and organic brown material into two separate layers in your compost bins. Make your organic brown layers twice as thick as the organic green layers. Wet your material so that it is as damp as a wrung-out sponge.
Stack boards over your hay bales to create working surfaces. Place tender plants on the boards. As the compost releases heat, the heat will drift upward and warm the plants.
Pull away the boards and check the compost daily with a meat thermometer that has a probe. The compost should remain between 120 and 160 degrees Fahrenheit. If the compost grows warmer, it will kill the microbes that are decomposing the organic material, and will slow down the decomposition.
Stir your compost with a pitchfork to shift undecomposed material to the middle of the pile whenever the compost's internal temperature drops below 120 degrees Fahrenheit.