by Bill and Mary Weaver
For the second winter, Ryan Pesch, of Pelican Rapids in northern Minnesota, has a new job description to add to his already lengthy list: deep winter greenhouse grower. In December 2014, he subtracted a job description: builder of deep winter greenhouse and root cellar.
Pesch, in his eleventh season on his 20-acre farmstead, has 15 years of experience as an organic grower. His other job titles include CSA grower and marketer (for 50 members in-season, and 17 members through the winter); farm stand operator from July to October; vendor at the Lakes Area Farmers Market; broker of his produce to other retail outlets; plus a full-time day job as an Extension agent for the University of Minnesota. He and wife Maree are raising three children, who are interested in the goings-on around them and finding ways to help.
Pesch seeded his first crop of cool season greens and roots on Christmas Day of 2014, just after finishing the final construction details. “I spent part of early December hanging off the roof to install two solar panels at the proper 60 degree angle for our latitude.” The solar panels indirectly heat water that is piped in a hot water loop to radiant tubing buried 1 inch deep in the sand floor.
Deep winter greenhouses, which are springing up in increasing numbers across Minnesota and Wisconsin, are defined as using minimal fossil fuel and having tall, steeply slanted glazing to catch maximum winter sun in the Upper Midwest. Typically these greenhouses have four-foot-deep rigid foam insulation in the soil around the perimeter, tight sealing of potential air leaks, and are built in lean-to style, with berming or protection from a building to the north.
Most have underground thermal storage, with fans blowing excess heat on sunny days into black plastic drain tiling wound through a rock layer several feet deep. The heat is then released at night. Many use lengths of plastic gutter with wooden sides as planters, hanging at different heights, to make best use of light from the tall (16’ high polycarbonate in Pesch’s case) passive solar glazing. Last year Pesch hung over 70 of these 3 1/2 foot long by 4” wide planters from rafters, but has calculated he can make maximum use of the available light by fitting in a total of 110 to 120.
Moisture in the greenhouse is less of a problem this year, after a CSA member sprayed insulating foam on the ceiling and back wall.
“These are not Eliot Coleman-type high tunnels. Coleman grows his crops to almost harvestable size before winter, then holds and harvest them through the coldest, shortest winter days.” In a typical deep winter greenhouse, temperatures are kept high enough by the construction methods and the back-up heat (in this case a wood boiler with propane as a last resort) to actually seed leafy veggies in winter, mostly Asian greens, including Pak Choi and Mizuna. Light is the limiting factor, not temperature. “Where it takes about 3 weeks to grow our braising mix in July, it takes 5 weeks from seed in winter.”
Pesch knows of at least 20 such greenhouses that have been built so far in Minnesota, with more in the works. Many of these owners were inspired by a book the University of Minnesota helped to fund — Northlands Winter Greenhouse Manual by Carol Ford.
With a young family to support, finances were a potential roadblock to the greenhouse. Pesch found a novel solution: a Kickstarter Campaign. “The website makes it easy. You go to Kickstarter and set it up. Kickstarter leaves it in your hands how to get people to the site. I spread the word to my CSA customers and by email and Facebook.
“One day, we became Kickstarter’s ‘Project of the Day,’ featured on page 1. We raised a total of $8,242, with 74 backers. Several of my generous CSA members contributed about half of that amount, but the contributions included smaller amounts from foreign countries from people I’d never met. While these individual contributions were not large, they helped to swell the total above our original goal, which was $8,000.” The Kickstarter funds paid for the active solar system, which Pesch installed himself. “If you’re not afraid of a little plumbing, it’s not difficult to do,” he noted.
The rest of the approximately $30,000 total cost was financed by an increased line of credit from their local bank, and by cash flow from vegetable sales during the summer and fall.
Pesch attached the greenhouse to the south side of his apprentice housing. The root cellar, entered through the greenhouse, is dug 12 feet into a hill.
This winter the root cellar holds a bumper crop of long-storing ‘Bolero’ carrots, purple top turnips, daikon, potatoes and Brussels sprouts. Pesch controls the temperature by opening or blocking the air intake. With 2015’s warm fall, the main problem was the initial cooling. “I actually put up a fan on a 6-inch tube to push cold night air. Once cooled, the root cellar holds produce at an ideal temperature.”
Excavation, new lumber and trucking rock for the thermal storage proved costly. Pesch has vivid memories of all the rocks he shoveled underground, and of carefully squishing the grouting between the polycarbonate and the wood framing to prevent air leaks.
“I have friends who built their deep winter greenhouse (which was smaller and had no active solar and no root cellar), for $6,000 by using a lot of “found” free materials and doing all the work themselves,” commented Pesch.
Pesch has found that for some winter-grown crops, it matters whether they’re planted pre-or post-solstice. “I plant lettuce, white turnips, radishes, Napa cabbage, and yukina savoy after December 21. Arugula bolts quickly in the lengthening days of late winter, so it is best planted pre-solstice. Don’t plan on getting more than one cutting from arugula. For many braising greens I try for two cuttings, then go to new plantings.”
Due to the deeply slanted glazing, although the greenhouse dimensions are 32X16, the growing space only extends 10 feet back. The extra 6 feet behind that, however, are welcome workspace for seeding, soil mixing, and produce washing and packing.
The 17 winter CSA members of Pesch’s Lida Greenhouse each receive seven CSA boxes: large ones at Thanksgiving and Christmas, and continuing boxes every three weeks through March. They are happy to purchase stored roots and fresh-grown greens from the same local, organic grower who supplies them in-season. Other customers are eager to snap up any extras. This past year with the warm fall, everyone received a bonus box with a bounty of late fall vegetables.
Northern Minnesota greenhouse grows fresh greens for CSA through winter
by Bill and Mary Weaver