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Serving Northern St. Louis County, Minnesota

Winter green

Deep winter greenhouse stays lush through the coldest part of the year

Marshall Helmberger
Posted 3/27/20

FINLAND—Nearly two feet of snow may still cover the ground here, but the growing season is well underway inside the deep winter greenhouse built in 2016 as a test site for the University of …

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Winter green

Deep winter greenhouse stays lush through the coldest part of the year


FINLAND—Nearly two feet of snow may still cover the ground here, but the growing season is well underway inside the deep winter greenhouse built in 2016 as a test site for the University of Minnesota.
It’s the many shades of green that first catch your eye as you walk inside the modest greenhouse that sits on a slight southerly slope just a block from what passes as downtown in this tiny community located about five miles inland from Lake Superior. Up against the glazed south wall, Swiss chard stands more than a foot high, where it’s managed to continue growing even in the short days of mid-winter. Nearby are hundreds of young heads of lettuce, looking lush against the backdrop of white outside. A wide variety of mixed greens are growing in hanging troughs built of rain gutter.
It’s a testament to the theory that where there’s a will, there’s a way, even when it comes to growing fresh produce through a long northern Minnesota winter.
That’s the idea behind a number of such greenhouses built around the state in recent years as a way to help U of M engineers and small-scale farmers better understand how to maintain a year-round growing season in Minnesota. The greenhouses, built in association with active farms, are still experimental, and university engineers regularly gather data and from them to assess how well they’re working. Based on what they’re learning they’re continuously making modifications to the design to make them more efficient and less costly to build.
The greenhouse in Finland, which is the 2.0 version, is the furthest north of any of the greenhouses and its relative success suggests that the design may eventually have commercial potential. Details and drawings on a new 3.0 version of the greenhouse are expected to be available soon, according to Stefan Meyer, who operates the greenhouse in association with Finland-based Round River Farms. Meyer grew up in the ag sector in southwestern Minnesota and worked on an urban farm in the Twin Cities before arriving in Finland. He’s studied permaculture and eco-agriculture for years, so he’s long been interested in alternatives to the industrial form of agriculture that’s taken root in much of the nation’s mid-section. Designing methods to maximize agricultural output from small sites is part of the mission of Round River Farm, founded by David and Lise Abazs, so the winter greenhouse experiment was a natural fit.
The theory behind the deep winter greenhouse is a simple one, which makes it distinctive from traditional greenhouses, notes Meyer. The glazing is located only on the south side, while the remaining walls and roof are well-insulated. That allows the greenhouse to gather most of the available sunlight to generate heat, while drastically slowing heat loss.
At the same time, heat storage is critical to the greenhouse’s efficient operation. Underneath the greenhouse floor is a three-to-four-foot thick layer of crushed rock. On sunny days, a suction fan pulls warm air from near the ceiling and conducts it through large diameter, flexible black plastic drain tile into the crushed rock. Overnight and on cloudy days, the warmth that’s built up in the crushed rock is ducted out into the greenhouse, providing a kind of “off-peak” heat supply. According to Meyer, the underground heat sink, which he calls his “battery” will last about three days without being recharged by the sun. Here in northern Minnesota, where sunshine in November and December is often in short supply, that requires a back-up heat source, run on electricity, to ensure that extended cloudy stretches don’t cause the plants inside the greenhouse to freeze.
Whether the produce grown during winter justifies the expense and carbon footprint of that electricity is a question that remains unanswered. But Meyer does manage to pack a lot of growing space in this relatively small greenhouse. Besides the large growing bed, Meyer has about 40 sections of rain gutter hanging from the ceiling. With a couple inches of dirt in the gutters, they provide an efficient way to grow large amounts of greens. Even in the depths of winter, Meyer says he harvests about six-to-ten large bags of lettuce and Asian greens, along with three bags of chard. It’s all bought and sold by neighbors through the local Organic Consumers Association.
The greenhouse is certainly scalable to a much larger operation, which could provide winter produce to a much larger population. As it is, Meyer estimates he spends just eight hours a week working in the greenhouse, so a single person could easily run a much larger operation than is possible with the relatively small prototype.
Bringing down the cost
Whether a deep winter greenhouse makes sense for other growers probably depends on the success of future versions. Meyer notes that the engineers who designed the earlier versions may have “over-built” them to some extent, which pushed construction costs much higher than might be financially-viable for many small growers. Construction costs have varied a lot, ranging from $22,000-$68,000, depending on a number of factors, which can be prohibitive when you consider the cost per square foot of growing space. The university’s extension service has developed some cost-saving ideas to help reduce that price tag. Growers who have the ability to do much of the work themselves can also bring the cost down considerably.
While the deep winter greenhouse is one worthwhile option for growers, the extension service notes that growers should fully assess their objectives before investing in building their own. Other season extenders, like double-layered high tunnels, can extend the growing season considerably, although they likely won’t keep plants alive during the depths of a northern Minnesota winter.
For more on designing and building your own deep winter greenhouse, Google: “deep winter greenhouse, University of Minnesota.” You’ll find plenty of information and plans available to help with your own project.


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