On a frigid winter day on the east side of Seneca Lake, the wind whips and the snow drifts, obscuring the two-lane roads crisscrossing white farm fields. Tractors stand still. Houses are buttoned-up and people scarce. Soft light filters through complete cloud cover. Trees, save for a few dark evergreens, are bone bare. The landscape appears dormant, if not bleak.

But looks are deceiving. In white structures rising up from the white snow, leafy greens are growing—or, if not growing exactly, waiting, in suspended animation for longer days and warmer temperatures. Just open the door, if you can get it past lumpy frozen mud and rocks, and peek under blanket-like covers. You might find tender spinach leaves spreading across the ground, or Swiss chard sprawling, or kale stretching upward.

Walking into these white structures in January, it’s a bit like time traveling a couple of months into the future, although this is hardly what you would imagine time traveling to look like. It’s spring in here, with new growth signaling warmer days ahead.

Known as high tunnels or hoop houses, these structures are the size of a building, and rather low-tech: a steel frame, staked into the ground, covered with tough, semi-transparent plastic sheeting. Unheated, but warmer than the outside weather.

Farmers here are no longer in the midst of the summer flurry of planting, cultivating, harvesting, and marketing. Liz Martin and Matthew Glenn of Muddy Fingers Farm are snug in their 1850s house a couple of turns o County Road 4—Liz typing a conference presentation on her laptop with her feet propped up next to the hot woodstove, Matthew considering what repairs need to be done on the greenhouse. A few miles south in Burdett, Aaron Munzer and Kara Cusolito of Plowbreak Farm are ordering supplies, planning for summer, and stealing a few free moments to go cross-country skiing.

But even in the winter, there is still work to be done. And, with the help of these high tunnels, their crops—spinach, mesclun salad mix, bok choy, mustard greens, and some lettuces—still need attention. The effort can pay off. In one January week, Plowbreak Farm reports harvesting between fifty and one hundred pounds of winter greens for wholesale. One chef responded to an email announcing February greens in enthusiastic ALL CAPS. Sara Caldwell, who operates Cheesy Rider sandwich shop and Global Taco truck, raves about their fresher taste and longer shelf life—and about the importance of keeping dollars in the local economy.

Muddy Fingers Farm expects an early spring harvest for farmers’ markets in Elmira, Corning, and Watkins Glen, where customers snap up greens as soon as they are available, looking for a leafy complement to their root crop staples such as turnips and carrots. “Spinach that’s grown over winter is sweet, it’s nutty, it’s fresh, really vibrant, versus something that’s come on a tractor trailer truck across the country,” says Liz.

To get that kind of quantity and quality during freezing weather, farmers must overcome the elements. Cold temperatures. Wind that’ll whisk away precious moisture. Frozen soil.

High tunnels are part of that effort and they represent a growing movement to grow local food indoors year-round. New technology, grant programs, consumer demand, and willing farmers are making winter growing more possible, more popular, and more pro table.

Protecting crops from the elements is nothing new, and people have always craved fresh food regardless of the weather. As far back as the first century, Roman Emperor Tiberius demanded his favorite foods year-round, and his gardeners created “beds mounted on wheels which they moved out into the sun and then on wintry days withdrew under the cover of frames glazed with transparent stone.” Greenhouses have been around for centuries. Around the world, gardeners use cold frames (usually a glass or plastic covering over a small garden patch). Blanket-like row covers are standard equipment for farmers.

But the advent of flexible polyethylene plastic during the twentieth century made greenhouses less expensive. And during the 1980s, experts at the University of New Hampshire and at Penn State began creating new high tunnel designs and researching best practices for growing, both simplifying and modernizing the greenhouse concept.

About fifteen years ago, Howard Hoover, Penn Yan vegetable grower and member of the Groffdale Conference Mennonite community, designed his first high tunnel.

“Did you ever sit inside a window on a sunny winter day and feel the heat and then go outside and feel that it’s bitterly cold? I didn’t have the money to build a proper greenhouse with plumbing, heating, ventilation, foundation, concrete—the whole nine yards—but in my steel shop I could make some hoops and stretch plastic over them to build a place that would be nice and warm on a cold day,” Howard explained to the Cornell Chronicle. He described his first attempt as a “sorry little affair.” But he saw promising results and began collaborating with Cornell Cooperative Extension specialist Judson Reid. Today, after many improvements, Howard’s family’s Evergreen Farm Shop manufactures easy-to-assemble high tunnels for sale to other farmers.

According to the latest census, New York State is home to 435 protected vegetable growing operations, including high tunnels, says Judson, adding that this represents over 100 percent growth from the previous five year period and a statewide value of over $27,000,000. The highest concentration of high tunnels in the state is found in the area between Seneca, Keuka, and Canandaigua lakes. Yates County alone has thirty-nine operators.

At Muddy Fingers Farm, the decision to invest in high tunnels, which range in cost from $3,000 to $7,000, was easy. The property is relatively small, at just over three cultivated acres, so using tunnels to extend the season means that they can plant six times per year, instead of just four. “They essentially create more space on the farm,” Liz says. Plus, some of their costs were offset by a USDA Natural Resources Conservation Service program that has helped fund more than 13,000 high tunnels and other protected growing environments since 2010.

On the day that Liz and Matthew erected one of their tunnels a few years ago, the ground was covered with snow, and they invited over a handful of helpful friends. Once the side frames were positioned, the crew muscled them upright, then added arching top bows for the roof. A steel bar across the length of the top added extra stability. Assembly was quick, with little more than people power, a wrench, and a ladder. Later, on a sunnier day, they rolled out a huge plastic sheet on one side of the structure, and then used a system of ropes and tennis balls to coordinate pulling the sheet gently over the frame. An ill-timed wind gust blew the plastic clear over the frame, forcing the crew to start over. But once the plastic was clipped taut with “wiggle wire” and the structure staked into the ground, it resisted wind just fine.

Today, Liz and Matthew have six tunnels, several manufactured by the Hoover family. With a tractor, they move some of the tunnels back and forth over their permanent vegetable beds, like pieces on a checkerboard, depending on which crop needs what conditions at a given time. Combined with row covers, they can raise the temperature about twenty degrees Fahrenheit compared to the outdoor temperature. Over time, they’ve experimented with different crops, kept detailed records, and determined dollar-per- minute investment in each crop. “Time is really valuable to us,” Matthew says.

Over at Plowbreak Farm, Aaron says it was a “giant surprise” that plants survive and thrive in cold weather. They started with high tunnels five years ago, and are erecting their fifth one this year. About a quarter of an acre of their cultivated six acres is under high tunnels.

“The tunnels totally change the climate,” Aaron says. The sunlight passes through the plastic, warming the air, plants, and soil inside the tunnels during the day. Then, as outside temperatures dip at night, the warmth from the plants and soil then radiates back into the tunnel. With a row cover acting like a blanket for the plants, that heat released from the ground is trapped, keeping the plants toasty—or at least alive.

Even during February “it’s green inside; it smells like soil,” Aaron says. It’s not exactly like four-season farming, he continues, because he can’t count on a big harvest every winter week. But the conditions inside make three-season farming possible, perhaps mimicking North Carolina’s climate during this time of year, he says. With an app on his phone connected to a sensor in a tunnel, he can check the temperature and humidity at any time. It’s not uncommon for the temperature to rise to eighty degrees Fahrenheit on a sunny spring day, only to drop to thirty degrees Fahrenheit at night.

Aaron says they try to grow everything possible—from greens to onions—as early as they can, with the first winter planting in late September. The scheduling requires careful planning. Summer tomatoes are kept in the high tunnels as late as possible, then Aaron’s team removes them all at once to prepare the soil for 5,000 new winter crop transplants, already greenhouse-grown in flats. Near the edges of the structure, they plant the most cold-hardy varieties, those whose leaves might actually freeze and then recover, and they protect the more tender varieties in the warmer inner rows. The aim is to harvest in late November, before the next round goes in the ground, for a total of two or three harvests per crop each until early March.

Without the tunnels, the November harvest would be the last until mid-May. Unlike outdoor farming, crops in the tunnels don’t have to be planted for staggered harvests. Thanks to their slow growth in the colder temperatures and lower light conditions, they can just sit in the ground as if they are in “living refrigeration.”

One crop Aaron is particularly excited about is Salanova lettuce. The seed catalogs boast that it’s “the newest innovation in salad mix production” and has longer shelf life than regular baby lettuces. Harvested as a dense head, its unconventional structure falls apart into separate leaves with one cut at the base, making it ideal for salad mixes. And, says Aaron, the flavor and texture is pleasantly lettuce-like and slightly bitter, as opposed to sometimes tasteless baby lettuce.

“We eat so much fresh salad in the winter,” he says, adding that Plowbreak Farm greens can be found at Dano’s on Seneca, Stonecat Café, Graft, and other restaurants. “People are starved for quality fresh greens in the winter, and they just adore these little leaves. People can be really emotionally connected to their food.”

Aaron concedes that the tunnels “aren’t a major profit center” for his farm, but they do provide a source of income that’s more stable than outdoor crops exposed to fickle weather.

“Winter greens production is not as lucrative as tomatoes or cucumbers, but can provide returns of up to two dollars per square foot in a time of year where farmers often have no revenue,” says Judson. Plus, at farmers’ markets, a beautiful display of greens during winter can attract consumers, who are then more likely to also buy potatoes or squash. “New York State is the national leader in winter farmers’ markets, with much of the local produce coming from high tunnels.”

The tunnels’ usefulness doesn’t end with springtime. “In this region tunnels are primarily used to grow delicious tomatoes, a month earlier than normal,” says Judson. “These crops are still grown in the soil and offer a wonderful alternative to shipped-in product.”

Heat-loving crops like tomatoes, eggplants, and peppers thrive in the tunnels, which can be cooled down if necessary by temporarily raising the sidewall plastic. Liz reports that their summer tomato plants have been known to grow enthusiastically to the ceiling and back down to the ground. In the protected environment, there is no worry about tomatoes splitting open or developing mold after a heavy rain—thanks to drip irrigation. And, the plastic excludes diseases like early blight.

For these reasons and more, Aaron calls the high tunnel the “backbone of the modern Northeastern vegetable farm.” 

Still, there are challenges, and these farmers temper their enthusiasm with realism. We’re still learning. We still feel like novices, they say.

For one thing, planting for winter crops must be done at the busiest time of the year: autumn. That’s when harvest is time-consuming, markets and CSA (community supported agriculture) shares are still going strong, and energy after a long summer season is waning, says Matthew. You can’t plant too early, or the crops will get too big and freeze, he explains. And you can’t plant too late, or they will be too tiny for harvest at the end of winter.

Controlling the climate variables is one of the benefits of using high tunnels, but it’s also one of the disadvantages because each variable must be properly managed. Irrigation must be controlled. Row covers must be added on freezing nights and removed during warmer days. And while some pests and diseases are more easily controlled inside the tent, others, like aphids, are still a problem.

Matthew admits that this year he and Liz let their Swiss chard—with its gorgeous, giant leaves—grow too big during a winter warm spell, only to witness the plants freeze days later, falling at and worthless on the ground. But despite the setback, the plants survived. From the center of each one sprouted a promising recovery: new, vibrant, rich green leaves, growing strong despite the icy cold outside. And they’ll be ready for harvest—and eating—right now.