Deep Winter Greenhouses and Year-Round Growing in Minnesota!

Nov 29, 2018

On Saturday December 8th, from 10 a.m. until noon, the Central MN Regional Sustainable Development Partnership, the Sustainable Farming Association of Minnesota, and Grampa G’s Farm in Pillager will host a public open house for a new Deep Winter Greenhouse.

Greg Schweser is Director of Sustainable Agriculture and Food Systems for University of Minnesota Extension Regional Sustainable Development Partnerships. He explains deep winter greenhouses this way:

“To get down to it, it’s a greenhouse that uses the sun’s heat--primarily the sun’s heat—stored in an underground rock bed, which acts as a heat battery to keep crops warm throughout the winter. This type of greenhouse we’re looking at lets farmers grow low-light and cold-hardy crops all winter with minimal use of external heat sources like propane (although backup heat is required), and with minimal external lights. So people are able to grow things like Asian greens, lettuces, brassicas like kale, chard, arugula—things like that—with very minimal external inputs.

“Farmers were experimenting with these deep winter greenhouses about five or ten years ago throughout Minnesota; a few pioneering farmers. They were looking to find ways that they could grow crops all winter long to provide themselves and their customers with product in particular areas of the state where, sometimes, fresh produce is harder to come by….That was the driving force of this technology. What the Regional Sustainable Development Partnerships do is work with farmers. They come to us with these ideas—these great, innovative ideas—and they come to us to help get the University of MN involved.

“So we worked with Carol Ford in the southwest region. She came to the University to help us help her, and we’ve done that. We’ve connected with the University’s Center for Sustainable Building Research and with horticultural faculty, and with students, and we’ve done a number of little projects on the deep winter greenhouse. It’s kind of gone from there.

“We went and visited a number of these winter greenhouses [that farmers had been using] and did some infrared scanning; we did some energy audits and tried to figure out all the different places that  we could tweak it and make it operate a little more efficiently. From those interactions we’ve created the blueprints and this prototype.

“One of the main notable differences is that this is a stand-alone greenhouse, where a lot of the other ones are greenhouses that people have affixed to the south edge of a garage or a barn or something like that. Ours is a stand-alone greenhouse, so it’s suitable for anyone who has southern/south access to the sun, whether or not they have an existing building they can attach it to.

“Also, our greenhouse has some of the functionality inside of it that works a bit differently from some of the older ones. Namely, we are collecting hot air from the peak of the greenhouse and sucking it into a rock bed with fans, where it’s distributed into a rock bed evenly through a manifold system on the north side of the greenhouse. The air is sucked through the rock bed on the south side where the fan is located… It’s a little bit more efficient than the older greenhouses some of the farmers were using where they were trying to push that hot air down into the ground and then having it dissipate through a soil floor. One of the things we’ve done is that we’ve sealed that soil floor with hard pan or concrete which allows the rock bed to fill up more efficiently and more completely.”

The University’s current research is on soil-based production systems rather than hydroponics or aquaponics because, according to Schweser, “the majority of people use soil-based production methods. For the most part people are doing soil, but that’s not the only way to do it. There are many ways to grow in a greenhouse.”

As part of the research project the folks at Grampa G’s farm are planning to focus on low-light, low-heat crops like brassicas and salad green mixes. “We’re doing that because that’s what a lot of producers are already interested in doing. Grampa G’s hasn’t started producing yet because this will be their first winter, so they’re just getting started. But others, in addition to the research with the university, are experimenting with things like ginger and turmeric, and some fruiting crops like tomatoes and green beans in certain areas of the state. That’s certainly possible if you add extra heat and extra light into this system. It can function like any greenhouse; you could grow anything. But for right now one of the things we’re focused on is what could be produced with minimal inputs.”

In terms of eventual impact, Greg Schweser says, “I like to think of it as, hopefully we’ll have the same sort of impact that high tunnels have had, or hoop houses. If you go through rural Minnesota it’s hard to see a small vegetable operation without a hoop house or a high tunnel. To me, that’s what made a local food system and a local food movement possible. That’s what enabled farmers north of a certain area to grow things like peppers and tomatoes in the first place. That really extended the summer season—the production season—by a couple months on either end of the summer. It helped farmers be able to grow a larger number of crops, a larger number of products, for a longer amount of time. It’s really been a game changer.

“I like to think of this system as the way to tie those ends of the production season together. So after your high tunnel season ends in, say, September, October, November—depending on where you are—then you can move into the deep winter greenhouse and start growing things from December, January, February, March; back into the other side of that high tunnel season. What this will enable farmers to do is create a year-round production system. If that takes off and it works, I think it could have a great impact. It could help farmers think of the entire season as a production season—not just summer and the spring—but really help people think about how they can grow all year around. And help them figure out how to best create a small farm system. Maybe people aren’t going to grow in the summer anymore when everyone else is doing it and there is so much more competition. This helps farmers look at their business in a holistic, year-round fashion.”

The open house at Grampa G’s farm is on December 8th from 10:00-noon. The event includes deep winter greenhouse presentations, a ribbon cutting and tour, and a question and answer session. Attendees are encouraged to RSVP with the Sustainable Farming Association at z.umn.edu/DWG_RSVP. Grampa G’s farm is located at 207 West Highway 10 in Pillager Minnesota.