March 10, 2013

Winter lettuce subject of study


WILLSBORO — To determine whether farmers can grow salad greens through the winter in Northern New York, the Northern New York Agricultural Development Program (NNYADP)-funded trials at the Cornell University Willsboro Research Farm in Willsboro are evaluating winter lettuce production methods.

A team of Cornell University researchers and extension specialists is investigating the use of prototype, low-wattage heating strips to warm the soil to enhance lettuce production during the winter months in Clinton, Essex, Franklin, Jefferson, Lewis and St. Lawrence counties.

With consumers willing to pay up to $12 per pound for lettuce-based salad mixes year-round, this research promises a high payoff value if the use of heat proves to be successful and cost-effective under the regional growing constraints.

Heating strips used

Cornell University Cooperative Extension Vegetable Specialist Judson Reid said the research in Northern New York is the first attempt at developing a system for heating the greens-growing environment inside high tunnels using heating strips primarily designed for in-floor radiant heat.

Amy Ivy, Cornell Cooperative Extension horticulture educator for Clinton and Essex counties, said that while spinach can be grown and harvested year-round in Northern New York with a minimal addition of heat largely in January and early February, lettuce crops are more cold-sensitive.

“Our question is can growers cost-effectively add heat to grow the salad greens year-round without sacrificing profitability,” she said. “There is great demand by consumers and by regional restaurants clamoring for local greens.”

Cornell University Research Associate Michael Davis explains that on clear, sunny days during the winter, temperatures inside a high tunnel can be 20 to 40 or more degrees warmer than the outside air, and, as a result, lettuce plants can be grown and harvested.

“The key to high-tunnel winter lettuce production is helping the cold-sensitive lettuce plants survive frigid nighttime temperatures,” he said.

Blanketed with row covers

To warm the lettuce-production beds during the night, either eight- or 15-watt electrical heat strips — prototypes not yet commercially available — were buried eight inches below the soil surface in the 30-foot by 96-foot Ledgewood pipe-frame high tunnels at the Willsboro farm.

To retain the heat around the lettuce plants, the production beds were blanketed with a double layer of rowcovers supported by wire hoops that straddled the growing beds and kept the insulating layers from touching the plants.

Black Seeded Simpson head lettuce plants were seeded indoors at the Carriage House Garden Center in Willsboro on Jan.1 and the seedlings were transplanted to the tunnels on Feb. 6. Five Star baby lettuce mix seed from Johnny’s Selected Seeds was planted directly into the high tunnel growing beds on Feb. 8.

Reid said it’s notable that on nights when the outdoor temperature dropped into the teens and single digits, the soil temperature at 1.5-inch depth in the heated lettuce beds with rowcovers never dropped below 40 degrees Fahrenheit, and the air temperature never dropped below 32 degrees.

“In contrast, the air temperature eight inches above the uncovered and unheated beds dropped into the low teens during the night of Feb. 12.”

The initial trial results provided insight on issues with the placement and width of the heat strips, the benefit of combining the heat strips with the use of low rowcovers, and the proximity of the lettuce plants to the high tunnel exterior.

“Low rowcovers were the big winners in this experiment as they markedly increased germination rates and lettuce production, even on growing beds that did not have heat strips in the soil,” Davis said. “On heated beds with low rowcovers, direct-seeded Five Star lettuce mix emerged three days ahead of the unheated beds with low rowcovers, and eight days ahead of the unheated and uncovered controls.”

“For direct-seeded lettuce, the days to germination and emergence is critical for maximizing the productivity of the high tunnel, and accelerated germination rates could be a significant benefit of the heat strip technology,” Reid added.

Lettuce was harvested from all the treatment beds on March 30, 2012.

Issues still remain

Ivy, who works with growers in Northern New York, cautions that while the heat strips provided a modest boost to lettuce production in the high tunnel, it is not clear that the heat strips make economic sense, and several problems with the heat strips need to be resolved.

The NNYADP-funded project provided two day-long programs for growers on winter crops production. Growers at those workshops indicated interest in winter production of fresh and storage crops, including greens, root vegetables, colored carrots, parsley root and celeriac.

The Cornell University Agricultural Experiment Station provided additional funding for the winter greens production project. The complete report is online under Horticulture: Vegetables on the NNYADP website at