Strawberries in May
By: Paul Bush
Otho Wells harvests strawberries from May 1 to June 15, at least six weeks before and for two weeks longer than is the norm in New Hampshire. Wells, professor of plant biology at the University of New Hampshire, developed this technique of overwintering strawberry plants under 6- to 7-foot-high plastic-covered tunnels, or hoop houses. While his method promises to support an important niche for market gardeners, ambitious home gardeners can benefit, too. It's not magic. Wells has simply adapted planting techniques long used in the South and West and added a hoop house.
Seven Steps to Early Harvest
The first week in October, Wells builds raised beds (10 inches high and 14 inches wide) within a series of tunnels at the university's horticulture farm in Durham, New Hampshire. He adds a 1-inch layer of compost to the soil, as well as any nutrients needed as indicated deficient by soil tests. Once the soil is ready, he tamps the beds with a sheet of plywood so the soil is firm and flat. He then lays drip irrigation hoses on the beds and covers them with black plastic, which he later cuts to insert plugs.
Black Plastic Mulch
The black plastic and the hoop house work together to keep both soil and plants warm. "When it's -15° F outside, the soil inside is only frozen 1/4 inch deep," says Wells. That means there's no need to mulch the plants to protect the strawberry crowns from winter cold.
As soon as the beds are prepared, Wells plants young transplants rooted from runners, or "plugs," of 'Chandler' strawberries. This, Wells notes, is the key to his success. "'Chandler' has superb quality," he says, "with good size and flavor and excellent productivity." Originally developed to overwinter in California, 'Chandler' has been shown to have a 99 percent survival rate in New Hampshire hoop houses, and it produces nearly a pound of berries-that's a level quart-per plant. Wells has tried several varieties and plant types, including northern-bred June-bearers and bare-root plants. Productivity of other tested varieties was significantly less, and bare-root plants proved much less winter hardy. Although 'Chandler' strawberries are early producers, gardeners seeking the earliest harvest can plant the variety 'Sweet Charlie' as well. Though not as productive, 'Sweet Charlie' ripens one week earlier than 'Chandler', around the last week in April. Wells emphasizes that strawberry plugs are essential to getting the strawberries off to a good start. The strawberries grow in the plug trays - filled with a peat moss and vermiculite soil mix - for four to five weeks. Unlike bare-root plants, the plugs are easy to slip through 2-inch by 2-inch slits in the plastic and their strong roots won't be damaged in the process.
Wells recommends planting in double staggered-rows with 12 inches between the rows and 10 inches between the plants in each row. Planted this way, you'll need 72 plants for a 30-foot bed.
Though he's only tested his system in southern New Hampshire, he believes the technique is viable throughout the North. "It'll work up to the Yukon Territory," he says, then pauses and backtracks a bit. "But if it gets to -30° to -40°, you might have to mulch the plants."