Grow Salad Greens In The Wintry Northeast?

With consumers willing to pay up to $12 a pound for lettuce-based salad mixes year around, this Northeast research promises a high salad crop payback.

Published on: Mar 26, 2013

Actually, there's no question that growing salad crops during Northeast winters will pay. What's more in question is what's the most economic way to do it.

Northern New York Agricultural Development Program-funded trials at Cornell University's Willsboro Research Farm is evaluating winter lettuce production methods. A team of Cornell researchers and Extension specialists is investigating use of prototype, low-wattage heating strips to warm the soil to enhance lettuce production.

Cornell Extension Vegetable Specialist Judson Reid explains: "This research is the first attempt at developing a system for heating the greens-growing environment inside high tunnels. We're using heating strips primarily designed for in-floor radiant heat."

HIGH TUNNEL WARM BEDS: Northern New York research shows salad crops can be grown during winter – under row covers, with prototype heat strips.
HIGH TUNNEL WARM BEDS: Northern New York research shows salad crops can be grown during winter – under row covers, with prototype heat strips.

Spinach can be grown and harvested year-round in Northern New York with a minimal addition of heat largely in January and early February, adds Amy Ivy, Cornell Extension horticulturist. "But 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. There's great demand by consumers and by regional restaurants clamoring for local greens."

On clear, sunny winter days, temperatures inside a high tunnel can be 20 to 40 or more degrees warmer than outside air. The key to high tunnel winter lettuce production is helping the cold-sensitive lettuce plants survive frigid nighttime temperatures.

The test
To warm the lettuce beds during the night, either 8- or 15-watt electrical heat strips – prototypes not yet commercially available - were buried 8 inches below the soil surface in the 30-foot by 96-foot Ledgewood pipe-frame high tunnels. To retain the heat around the lettuce plants, the beds were blanketed with a double layer of row covers supported by wire hoops straddled the growing beds. That kept the insulating layers from touching the plants.

Simpson head lettuce plants were transplanted to the tunnels. And Five Star baby lettuce mix seed from Johnny's Selected Seeds was planted directly into the high tunnel growing beds on February 8.

"It is notable that on nights when outdoor temperature dropped into the teens and single digits, the soil temperature at 1.5-inch depth in the heated lettuce beds with row covers never dropped below 40 degrees Fahrenheit. Air temperature never dropped below 32 degrees.

In contrast, the air temperature 8 inches above the uncovered, unheated beds dropped into the low teens.

Low row covers inside the high tunnels were the big winners. They markedly increased germination rates and lettuce production, even on growing beds that didn't have heat strips in the soil.

On heated beds with low row covers, direct-seeded Five Star lettuce mix emerged three days ahead of the unheated beds with low row covers, and eight days ahead of the unheated and uncovered controls.

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

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

The complete Cornell report is online under Horticulture: Vegetables at www.nnyagdev.org.