It is winter in northern Minnesota, and the outdoor growing season is long gone. But leave it to Minnesotans to invent a way to grow greens in the winter using materials you can easily get up here. Lumber, glass, big rocks, dirt, and sunshine is all you need for a Deep Winter Greenhouse.

The Deep Winter Greenhouse (DWG) has gone through several re-designs, but it all started with a book by Carol Ford and Chuck Waibel in 2009 titled The Northlands Winter Greenhouse Manual. They lived in Chippewa County, Minnesota, several hours south of here, but the idea caught on with growers in the far north too.

So, what is a DWG? It is a passive solar greenhouse that captures the sun’s light and heat during the day and stores the heat it in the earth to recirculate at night. The greenhouse is oriented east-west with a large south-facing glass or polycarbonate wall built at an angle that will catch as much of the sun’s energy as possible, given the latitude. The other walls are solid and very well insulated, often with reflective interior surfaces, and the north wall is sometimes earth sheltered, if the landscape permits. It is the dirt, and sometimes gravel or large stones about four feet deep under the greenhouse, that act as a battery to store the heat that’s captured during the day. That heat is blown underground with a fan and then ducted out and up into the growing area at night.

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