Even in late November, Dawn Pape’s newest garden was a welcome sight for winter-weary eyes.
In her Shoreview yard, under a blanket of snow, is a polycarbonate-topped, 2- by 8-foot box — or “cold frame.” Brush aside the show, lift the lid, and inside was an improbable vision: healthy spinach, kale, salad greens and other veggies growing in the frigid ground.
“It’s so uplifting to see green when it’s kind of bleak outside,” said Pape, a master gardener and garden-book author, who was still harvesting around Thanksgiving — and hoping for at least a few more weeks of homegrown produce. “If I can make it to Christmas, I’ll be pretty happy,” she said.
Cold-weather gardening is not for everyone, but a hardy few are giving it a try.
Some are market gardeners who erect plastic-covered shelters (often called hoop houses or high tunnels) so that they can produce food earlier in the spring and later in the fall. Urban agriculture consultants Cherry Flowers and Tim Page of Page & Flowers (www.pageandflowers.com) grow vegetables in high tunnels at their home in St. Paul and at an apartment in Minneapolis that serves as their office. They sell their produce at the Mill City Farmers Market.
“In the spring, you can get a jump on greens, even in March, and have them ready for the May farmers market,” Flowers said.
Pape is growing on a very small scale, just for her family’s table.
“I’ve read about it [cold-frame gardening] for several years and decided to try it,” she said. She found a kit online (at www.gardeners.com) that was the same size as one of her existing garden beds, ordered it and installed it in the fall, surrounding it with straw bales for extra insulation.
Cold-frame gardening has its limitations in Minnesota, she’s discovered. “The harvest’s not as plentiful” as during the regular growing season. Plant growth is minimal. “You’re not really gardening, just sort of picking. It’s basically a refrigerator.”
But Pape enjoys the challenge of pushing the growing season to its outer limits. “It’s thumbing your nose at Old Man Winter,” she said.
Extending the season
Hoop houses and high tunnels are a familiar sight in many rural areas, but now more urban dwellers are experimenting, inspired by the local food and urban agriculture movement.
“There’s more interest in extending the season,” said Flowers, who, with Page, consults with schools and other organizations on urban-growing options.
Long before locally produced food became trendy, the University of Minnesota and Penn State were collaborating on cold-weather growing research, according to Terry Nennich, U of M Extension professor, fruit and vegetable production.
“We started with basic vegetable production, to see how far you could extend the season,” he said. “Now we’re moving into fruit.”
Nennich has seven high tunnels at his home near Bemidji, where he and his wife grow a wide variety of vegetables, even heat-loving tomatoes, cucumbers and peppers. “You can extend the season four to five weeks at the beginning and at the end,” he said. “Even a small high tunnel will produce a tremendous amount of food for a family.”
The plastic-covered structures differ from greenhouses in that they’re usually considered temporary, without rigid walls and typically without mechanical ventilation or heat.
But heat-enhancing options are available. Some growers use solar heat, or warm the soil with an electrical coil, Nennich said. Page and Flowers have a large pallet of compost inside their Minneapolis high tunnel, and that helps generate heat as it breaks down, they said.
If you want to try offseason growing at home, siting is crucial, according to experts. Choose a spot that gets maximum sunlight. Minnesota cold isn’t the only obstacle to winter growing; so are shorter days and longer nights. “It’s not just temperature. It’s length of day, angle of the sun,” said Nennich. “We get into fall, December, we don’t have much daylight.”
You’ll probably have much better luck with cold-tolerant plants such as greens, Brussels sprouts and cabbage than you will with plants that need a lot of sun and heat, such as tomatoes and peppers.
You can buy a cold-frame kit, as Pape did, or go the DIY route. “There are books with instructions,” she said. “Some people say, ‘Just use old windows.’ ” But she opted to save time and aggravation. “I’m not handy, and I have kids,” she said. “This took a half-hour and a couple hundred dollars.”
High tunnels also can be a DIY project. “If you’re handy, you can make one,” said Nennich. But be sure to use the right materials. “I warn people, you’ve got to use greenhouse plastic” from a greenhouse supplier, rather than basic plastic from a hardware store — “unless you want to replace it every year.”
And while cold-frame gardens have a low profile and can be installed just about anywhere without ruffling neighbors’ feathers, high tunnels and hoop houses can be another story.
Many municipalities have rules and restrictions governing their use in residential areas. In Minneapolis, for example, hoop houses were addressed in the Urban Agriculture Zoning Text Amendments passed in 2012; basically the amendments allow hoop houses in residential back yards, at heights up to 12 feet, for up to 180 days a year, provided they meet setback and building-code requirements.
Even though Pape is an experienced gardener, she’s a “rookie” when it comes to winter growing, she said. “I keep expecting everything to be a total flop.” The experiment was going better than she’d expected — until Dec. 6.
She discovered that rodents had tunneled their way into the cold frame and devoured her harvest. “Live and learn,” she said. “Next year, I’ll be installing hardware cloth below ground.”