This is the first of a series of articles highlighting agriculture in the Midcoast. Each month, the article will highlight one of the products available at that time of year, and profile some of the farms that are raising it.

If you think you have to wait for bounteous summer farmers markets to get local produce, you may be wrong. A few area farms have already begun their harvests. Using cold frames, these enterprising growers are growing early crops of greens and roots to satiate those who cannot stand to wait for locally grown produce. And in doing so, they are stretching the seasons within which Knox County can feed itself.

Rose Thomas of Dolce Vita Farm in Lincolnville has been growing crops under cover for five years. She got into the craft unintentionally. When a car accident left her on crutches, she grew tired of sitting around doing nothing.

“I couldn’t sit around waiting,” she said.

Rose started a garden. Soon she had more vegetables than she and her husband could use, so they decided to start selling some. Her husband, Peter, built a small market stand on the edge of their driveway of rough cedar with a roof made out of leftover rubber. Peter also built her the first hoophouse and Rose began growing vegetables through the winter.

This kind of farming is called season extension. The farmer builds a frame over a bed of soil and covers the frame with a material clear enough to allow sunlight in. If the structure is not heated with a stove, it is called a cold frame. Cold frames can be as complicated as a full-scale greenhouse with room to walk around in or as simple as a glass window over the soil resting on walls made of hay bales. There are thousands of designs; some are professionally assembled and others are cobbled together with ingenuity and whatever is lying around.

No matter what the design, it all works on the same principle: sunlight shines through the outer covering and becomes heat when it strikes the ground, and that heat escapes the structure at a slower rate than it accumulates during the day. Maine gets the same amount of sunlight as the warm Mediterranean region, and by using season extension methods to trap heat, farmers can create similar climates.

As her customers increased, Rose added several greenhouses and built a new market stand. She refined her production to focus on greens and root crops in the winter.

Rose took me one day into one of her first greenhouses, a 48-foot-long structure with a peaked Gothic arch. We walked down a wood-chip lined path in the center. She was planting one side of it with spinach and mache greens, using a long straight 2-by-4 to mark between rows and pat down the soil. Although it was a cold, cloudy and blustery day in March, the greenhouse was comfortable inside.

When planting crops for winter production, “it’s all about timing,” Rose said. “You have to plant it before it gets too cold.”

Seeds will only germinate if the soil temperature is warm enough; once it gets below 55 degrees, most seeds will lie dormant until spring. Rose plants her first crop from the end of August to December, then begins planting again in February.

As we walked through Rose’s greenhouse in late March, she lifted floating row cover (a white fabric designed to keep plants and soil even warmer) off her crops to show me her burgeoning harvest: arugula, chicories, radicchios and lettuces with colorful names such as Winter Wonderland and Lolla Rossa. In the corner, early tomato plants huddled beneath buckets, sheltered from the dropping temperatures outside.

A funny thing happens in winter to many of these plants, especially those in the Brassica family, such as arugula and kale. These plants are winter annuals, meaning they naturally grow foliage in the fall, overwinter, then bolt (go to seed) in the spring. During the winter, they buckle down and bulk up on nutrients in preparation for spring bolting. Their leaves acquire a deep texture of sweet and nutty flavors you simply can’t get from greens grown on the other side of the calendar — or the country.

Rose gets a peak harvest of greens in April, then begins pulling those crops out and replacing them with tomatoes, peppers and eggplant in May.

“A lot of the crops that I grow are cold crops from Italy,” said Rose. “Anything that can overwinter outside in Italy can overwinter under cover here.”

Rose and Peter are now expanding their business. For instance, they plan to plant raspberries under cover to get an extra crop each year. And they are experimenting with strawberries as well. Rose is teaching a course on season extension for the Five Town Community School District Adult Education Program.

Rose is not the only grower to use season extension in the Midcoast. The Natural Resource Conservation Service recently administered a grant to help local farms put up high tunnel cold frames.

“We had a very strong response,” said Mary Thompson of the Natural Resource Conservation Service. “It’s an emerging technology. It’s been around for years, but now people are catching on that it can help them make a go of it.”

Thompson said retired people are staying longer on the coast, and thus buoying the markets for local produce deeper into the fall.

Look for more and more farmers to use season extension techniques in the coming years. The technology is getting cheaper. For instance, Johnny’s Selected Seeds has recently come out with a “pipe bender” tool for shaping electrical conduit into small hoops to use to make low tunnels (low tunnels are like miniature greenhouses, too small to walk in but warm enough for growing). The company claims growers will be able to achieve greenhouse-level protection for 5 percent of the cost.

Larry Miller of Miller Farm in Rockport has purchased a bender for making larger hoophouses out of round metal stock. He has built one 12-by-24-foot house this way and is currently trialing different kinds of crops in 4-by-4-foot patches. He has just started harvesting mesclun and got 5 pounds out of one cutting from one patch. He hopes to get three cuttings each spring.

If you’re craving fresh, nutritious produce this spring, check with your local vegetable farmers to see if they’re growing any in their greenhouses. Soon, buying locally grown produce in the winter and spring may not be considered an oddity; it will be a normal course of habit for consumers who desire the freshest flavors and nutrients their region can provide, all year-round.

Jed Beach works for Aldermere Farm in Rockport and is raising awareness of local farming in the Midcoast.