Garden Chat

By Jean Lundquist

This deep winter greenhouse can be found at Alternative Roots Farm near Madelia. The $38,000 investment will help them grow year-round.

Exploring a deep winter greenhouse

There are so many different kinds of greenhouses, with so many different uses.

My 9-by-12 greenhouse was never intended to try to keep producing tomatoes and peppers yearround. Yet, it was fun to extend the season for both past Thanksgiving. With the help of a small space heater, I brought in the last of the tomatoes and peppers and unplugged the heater for a few months until the seedlings take residence.

Mid-December we feasted on the last of the vine-ripe tomatoes and peppers. We are so spoiled, I considered tucking a tomato into my purse and carrying it with me whenever we went to a restaurant that put tomatoes on a sandwich or salad and asking them to use ours.

There’s just no comparison with traditional winter tomatoes that look and taste like cardboard, if they taste like anything at all.

But placing my greenhouse into hibernation, while depressing, got me interested in another kind of greenhouse called a “deep winter greenhouse” or DWG. Research took me to visit the organic Alternative Roots Farm near Madelia.

I had expected to find a sort of underground bunker with a transparent top letting sunshine in. I’ve read that in many neighborhoods in cities, neighbors often complained about how unsightly these contraptions are and how short-lived for that reason.

Instead, I found a smart, neat, good-looking structure that was not underground, as far as I could tell. Operated by Brooke and John Knisely with help from toddler Leo, it appeared at first that I had been duped.

But this engineering marvel was indeed what I had been expecting, in terms of using the warmth of the earth and the sun to grow food.

With a grant from the University of Minnesota Regional Sustainable Development Partnership, the area Brooke refers to as “my happy place in the winter” was born.

It started with an excavation 4 feet deep. That was filled with small rocks that capture and trap heat from the ground. Landscape fabric and gravel atop that bring it almost to ground level, so there really isn’t a descent to get into the greenhouse. (This is a very simplified explanation of how the greenhouse works.)

The day I visited, the temp outside had not yet reached 10 degrees F, but inside, the air was warm and comfortable enough that Leo shed his mittens and coat to play.

Because the grant required very specific design elements, the Knisleys hired the work to be done rather than doing it themselves. The final price tag for the 24-foot-by- 24-foot structure, with a 16-foot-by-24-foot growing space, was nearly $38,000.

Brooke said a neighbor is in the process of building a similar structure, which he is doing himself, including

digging the pit by hand. “I know it can be done for less,” she said. All of the prototype designs for these DWGs are online from the U of M.

This is her fourth season in the DWG, Brooke said. The “season” she is referring to is winter, or September to April, depending on weather. While there is auxiliary heat in the DWG, the cost is minimal because of the design and its efficiency. The slant of the roof, for example, “is designed to capture the most sunlight on the shortest day,” she said. Also, ducts that capture heat in the peak of the structure funnel warm air back into the rocks beneath the floor to recharge their heat.

There are dozens and dozens of flats and other containers in the Alternative Roots Farm DWG. Brooke sells the microgreens, salad greens and pea shoots at the Mankato Farmers’ Market, her on-site Farm Store, and to some local restaurants, plus some Consumer Supported Agriculture customers.

When the winter season ends, Brooke will start bedding plants to put in her DWG to sell to local nurseries. Brooks Knisely and son Leo are pictured here inside the family's deep winter greenhouse.

Oh, the joy of a greenhouse, all year long!

Jean Lundquist is a Master Gardener who lives near Good Thunder. gardenchatkato@gmail.com

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