Imagine going outside to your garden during February in Minnesota and being able to pull fresh lettuce or strawberries from the ground. No, you’re not dreaming. In Northeast Minneapolis, some gardeners have been experimenting with the concept of growing things in winter: the walipini.
The walipini is a greenhouse that uses underground insulation to gather warmth in the winter months. The light source is filtered through the sheets of plastic that covers the greenhouse, and since there is no glass involved, the walipini is much more affordable than an above ground glass greenhouse.
The Benson University at BYU shares some tips on the structure a walipini:
The Walipini utilizes nature’s resources to provide a warm, stable, well-lit environment for year-round vegetable production. Locating the growing area 6’- 8’ underground and capturing and storing daytime solar radiation are the most important principles in building a successful Walipini.
The Walipini, in simplest terms, is a rectangular hole in the ground 6-8′ deep that’s covered by plastic sheeting. The longest area of the rectangle faces the winter sun — to the north in the Southern Hemisphere and to the south in the Northern Hemisphere. A thick wall of rammed earth at the back of the building and a much lower wall at the front provide the needed angle for the plastic sheet roof. This roof seals the hole, provides an insulating airspace between the two layers of plastic (a sheet on the top and another on the bottom of the roof/poles) and allows the sun’s rays to penetrate creating a warm, stable environment for plant growth.
This infographic shares more facts on walipinis:
Back in Northeast, the Minneapolis residents have named their walipini Sophia. The structure was constructed from donated materials, including pallets and playground lumber, old fencing and reclaimed windows. The Star Tribune says, “The makeshift structure utilizes passive-solar design — the sun comes through the glass windows and hits the north wall, where stones and buckets of water are placed to absorb heat. On a recent day, when the outdoor temperature was about 20 degrees, the temp inside the walipini measured 44 degrees, and the soil close to 50 degrees.”
With the push to find more ways to extend the growing period and source locally, walipinis may be where the industry is moving. “There is this push — we do need to find low-tech, low-cost ways to grow food year-round,” said Paula Westmoreland, an agroecologist and permaculture designer who founded the Permaculture Research Institute-Cold Climate and now operates Ecological Design in Minneapolis. Passive-solar greenhouses above ground are more common in Minnesota, she said, but she’s heard about walipinis in recent years, and visited one in Wisconsin that was successfully producing food. “People will continue to experiment.”