Pit Greenhouses or Walipinis Come In All Sizes and Styles
Depending on latitude, but despite above ground air temperatures (and wind chill), 6 to 8 feet down into the earth, temperatures remain fairly constant, between 50 and 60°F. Meaning your pit greenhouse will be much warmer than an above ground greenhouse in winter and that cool earth will keep temps bearable in the summer.
Pit greenhouse in Spetchley Gardens, UK. Stairs down to entrance on right. Image byMezzapod.
Underground greenhouse. The inside can be cased in stone, mud brick or any dense natural material able to absorb large amounts of heat. Cool weather crops like lettuce, kale and brocolli can be grown during winter in harsh climates. The glazing creates a “greenhouse effect.” If your water table is high, obviously that could spell disaster. It is recommended you build your greenhouse at least five feet above the water table. growtest.org
Mike Oehler’s pit greenhouse design. Mike digs a deep trench for access on the shaded south side which also allows cold air to sink and be warmed by the deeper, warmer soil. Many install tubes within the soil to transfer warmed air into the earth, yet Mike believes you need only the cold sink to allow the transfer in most climates.
Called a walipini in South America (from the Aymara Indian language, meaning "place of warmth"). As you dig, save your upper most topsoil (for the new bottom) and use the deeper soil as the new berm on the north side (or south side if you're south of the equator). Angling your window 90 degrees to the sun on the winter solstice will allow the pit to store the most heat during those days when the sun shines the fewest hours. Benson Institute Building a Walipini: www.bensoninstitute.org
Earthbag pit greenhouse. During the day, the earth walls store heat, the walls are the battery that release their heat at night. A properly designed pit greenhouse is naturally warmed at night from five sides, in an above ground greenhouse, only one side, the floor is heated during the day. A waterproof barrier extending along the periphery and down the berms are necessary www.naturalbuildingblog.com