What are Pit Greenhouses?
What are pit greenhouses, also known as underground gardens or underground greenhouses? In simple terms, pit greenhouses are structures that cold climate gardeners use to extend the growing season, as underground greenhouses are much warmer in winter and the surrounding soil keeps the structure comfortable for plants (and people) during summer heat. Pit greenhouses have been constructed in the mountains of South America for at least a couple of decades with tremendous success. The structures, also known as walipini, take advantage of solar radiation and the thermal mass of the surrounding earth. They are also widely used in Tibet, Japan, Mongolia, and various regions across the United States. Although they sound complex, the structures, which are often built using repurposed material and volunteer labor, are simple, inexpensive and effective. Because they are built into a natural slope, they have very little exposed area. The structures are usually lined with brick, clay, local stone, or any material dense enough to store heat effectively.
Underground Greenhouse Ideas
Building an underground pit greenhouse can be accomplished in various ways, but most pit greenhouses are usually basic, functional structures without a lot of bells and whistles. Most are 6 to 8 feet (1.8 to 2.4 m.) deep, which allows the greenhouse to take advantage of the earth’s warmth. It’s possible to incorporate a walkway so the greenhouse can also be used as a root cellar. The roof is angled to provide the most warmth and light from available wintertime sun, which keeps the greenhouse cooler during the summer. Ventilation keeps the plants cool when summer temperatures are high. Other ways to optimize heat during the winter months are to supplement light and heat with grow lights, to fill black barrels with water to store heat (and to irrigate plants), or to cover the greenhouse roof with an insulating blanket during the coldest nights. Note: There’s one important factor to keep in mind when building an underground pit greenhouse: Be sure to keep the greenhouse at least 5 feet (1.5 m.) above the water table; otherwise, your underground gardens may be a flooded mess.
