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Thu March 21, 2013
Spring May Have Sprung, But Most Gardens Are Still Slumbering
For vegetable lovers, the start of spring can be a cruel tease, hinting of a feast of just-picked peas and spinach and beets, but delivering instead tired iceberg and romaine shipped from distant climes.
"It's zero here right now," Terry Nennich reported Wednesday morning, the first official day of spring, from Grand Rapids, Minn. So much for spring. Not only was it well below freezing, but the ground remained blanketed by 2 feet of snow.
Nennich is a veggie guy, a horticulture research director at the North Central Research and Outreach Center of the University of Minnesota, which stands about 120 miles from the Canadian border. Undaunted by the fact that spring still looks a lot like winter, Nennich takes the bringing of vegetable bounty to the northland as a personal and professional challenge.
"We have plants ready to grow in the ground," Nennich says. "Those beet and onion seedlings were started in heated greenhouses and are just waiting for enough warmth to transplant."
Across the country, commercial vegetable growers and home gardeners are trying to gauge the impact of a cold, wet spring, balancing the itch to plant with the knowledge that flirting with spring's whims can bring heartache.
Sun isn't the problem. By March, even northern Minnesota has enough daylight for plants to grow. The problem is cold.
Hardy spring crops like spinach and kale can freeze solid in a late cold snap, thaw out and keep right on growing. But to start out, even the tough ones need earth that's warmed up to 45 or 50 degrees for seeds to sprout. Plant too soon, and seeds rot. The few plants that do grow remain puny and vulnerable to disease.
So impatient growers hustle the warming process along with blanketlike polyester row covers and plastic-covered high tunnels, which are like unheated Quonset huts. (We've chronicled how growers Zach Lester and Georgia O'Neal use these techniques to keep greens growing all winter long through snow and frost in Unionville, Va.)
Growers in Minnesota have embraced these techniques over the past decade, extending the growing seasons by 30 percent. They can start selling locally grown spring vegetables to farmers' markets and restaurants two months earlier, Nennich says. "There's a big market in the restaurants for local greens."
But high tunnels don't warm the soil enough to accelerate less hardy crops like tomatoes, peppers and cucumbers. Their seeds won't sprout unless the earth is 60 or 70 degrees, and they shrivel at a hint of frost.
So Nennich and his colleagues are attacking the problem at its roots, with solar-heated soil.
They run corrugated plastic drainage tubes through the soil under hoop houses, and connect the tubes to solar panels. Warm air is pulled by a fan all winter long, countering the region's bitter cold; it can thaw icy soil by March 1 and banish frost by mid-March.
Nennich and his colleagues are working on perfecting the solar soil heater design so it's cost-effective. He envisions a future when fruit trees grow in solar-heated tunnels, bringing a touch of Georgia to the far north.
But for now, he'd be happy to see spring.