enlarge Gregory Rec/Staff Photographer

Jeff Tarbox picks Tuscan kale in a greenhouse at Sunset Farm Organics in Lyman on Thursday. The farm sells more than 300 pounds of vegetables weekly through the winter to Portland restaurants, at a farmers market in Brunswick and through a community-supported agriculture program.

enlarge Gregory Rec/Staff Photographer

Kay Fowler, right, of Spring Brook Farm in Cumberland, sells beef to Susan Howe at the farmers market in Falmouth last week. The farmers market will continue through the winter. Most winter farming in Maine is being done on small existing farms.

enlarge Gregory Rec/Staff Photographer

Paul Lorrain started Sunset Farm Organics in Lyman in 1990. Over the years, he has developed a system for growing vegetables in greenhouses throughout the winter. He operates eight greenhouses between Oct. 1 and the end of April.

enlarge Gregory Rec/Staff Photographer

Cordelia Lane of New Elm Farm in Freeport spins yarn at the farmers market in Falmouth last week. Lane sells vegetables at the market in the summer but is selling knitted items through the winter. The number of winter farmers markets in Maine has doubled in the past year to more than a dozen.

The vegetable-growing season used to end with the first hard frost in Maine.

Not anymore.

An increasing number of farmers are pushing the growing season into the winter to take advantage of the surging demand for locally grown food. As a result, more farmers are operating greenhouses, branching out into cool-weather crops and creating new markets for their produce.

"Basically, people have gotten into it because their infrastructure is already there," said Mark Hutton, vegetable specialist and assistant professor of vegetable crops with the University of Maine Cooperative Extension.

Winter farming was pioneered in the 1990s by organic farmer and writer Eliot Coleman and his wife, Barbara Damrosch, at their Four Season Farm in Harborside. The two took a trip to Europe in 1996, following the 44th parallel through France and Italy – the same latitude as Maine – when the idea of winter farming hit Coleman.

"The whole time, we had seen gardens in January with Brussels sprouts and leeks, and the minute we got above the snow line there was nothing," said Coleman.

Coleman said he realized there was plenty of sunlight in Maine during the winter to grow vegetables – he just had to modify the temperature. So he came up with the idea of layered greenhouse structures that require minimal or no heating.

While there are no recent statistics on how many Maine farmers are venturing into winter gardening, agricultural experts say the number of new winter farmers markets and winter community-supported agricultural ventures reflects the increase.

There are about 18 community-supported agricultural operations selling winter shares of organic crops raised on Maine farms, according to the Maine Organic Farmers and Gardeners Association. The organization has seen its list of winter farmers markets more than double in the past year to more than a dozen across the state.

Other farmers markets are extending their seasons, including the Portland Farmers Market in Monument Square, which is staying open a month later than in past years.

Just why winter farming was not widely practiced before is a bit of a mystery.

Coleman said it could be that people simply assumed vegetables wouldn't grow when there is snow on the ground.

Hutton attributes the practice's growth to the advent of the locally grown movement in reaction to the rise of global corporate marketing, creating a demand that farmers are now rushing to fill.

Paul Lorrain, who raises lettuce and other vegetables in the winter at Sunset Farm Organics in Lyman, said it probably was just that vegetable farmers burned out in the summer and needed the winter to recuperate.

A landscaper in the summer, Lorrain has been steadily expanding his operation since he started in 2000. His first greenhouse was unheated. But after a two-week stretch of cloudy, minus-20-degree weather destroyed his crop, he started heating his greenhouses with propane to 37 degrees.

Today he operates eight greenhouses between Oct. 1 and the end of April, harvesting about 300 pounds of produce a week. He sells it to local restaurants, at a winter farmers market in Brunswick and through a new community-supported agricultural operation based at Wolf Pine Farm in Alfred.

"We have gone from not being able to give it away to not being able to grow enough," Lorrain said.

Tom Harms, who runs Wolf Pine Farm with his wife, Amy Sprague, left his job as a computer programmer this year to manage the winter community- supported agricultural venture at the farm, which until last winter sold shares of the harvest only in the summer.

"We are not just extending the season, we are making the winter our whole business," Harms said.

If all goes well, next year the farm will grow vegetables just for distribution in the winter, he said.

Harms has sold 350 shares this winter, signing up summer customers...