Monday kickoff: How to grow salad in winter

As winter comes to a close, farmers and researchers interested in growing cold weather greens are taking a look back at what worked, and what didn't this season.

We got a news release from the Northern New York Agricultural Development Program recently asking, "Can farmers grow salad greens through the winter in Northern New York?"

I put in a quick call to Dan Kent of Kent Family Growers to find out.  He tried growing greens for their winter CSA for the first time this year, "It was good enough, but not as good as I had hoped."

The Kent's greenhouse is heated from the floor, with radiant cement slabs. It's covered with 8 inches of soil, to give the plants room to move their roots. Dan Kent says they wound up with small heads of lettuce for their CSA members in late December, "The romaine was loose, not a tight head, not big, heavy, and thick." He says the Chinese cabbage was delicious, but also small, loose heads.  Kent says:

"Things don't grow when daylight is less than 10 hours a day. That happened around the third week of October. The greenhouse, this winter, had heat. I thought that would override the daylight issue, and we would get more growth. But they didn't grow much at all."

Kent heated with wood, which he says didn't cost nearly as much as electricity or oil, but was a lot of work, "I spent weeks gathering."


Cornell's research

The NNY Ag Development Program funded a study by Cornell University and Cooperative Extension.  Experts grew lettuce in unheated high tunnels using low-wattage heating strips to warm the soil.

In a press release, 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."

Some of the lettuce beds were blanketed with a double layer of rowcovers(supported by wire hoops), to retain the heat around the lettuce plants. Some beds were not covered, for the experiment.

Cornell found a variety of factors were significant in how well the plants grew, "…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."

Lettuce ready for harvest March 30, 2012 in Willsboro Research Farm high tunnels. Photo: Michael Davis

They had one finding similar to Dan Kent: the biggest factor was not the heat strips. Cornell's Michael Davis says,

“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.”

This is obviously a learning process, but it's possible, and there is good financial incentive to get winter lettuce programs off the ground in NNY.  Dan Kent says in Albany, New York arugula can go for $48 per pound in the winter!  North Country customers may not have that kind of bank (or irrationality), but many are certainly willing to dig deep for locally-grown winter greens.

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  1. Of course, Eliot Coleman in Maine has been growing winter greens for years. The trick is to plant them in August (or even late July) so they have time to mature before day length drops below 10 hours.

    Coleman has written several books on the subject for market gardeners. I've tried growing winter greens myself in my home garden cold frame and the planting dates are absolutely critical. Miss those and the whole thing falls flat. You also have to allow for a longer window until harvest ("days to maturity") because as the days become shorter, plant growth slows.

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