Learning to garden in four seasons – rather than one (summer) and fragments of two (spring and fall) – can be a bit like learning to think in four or five dimensions. But the rewards, say Colorado gardeners Rick and Shirley Visser, are mind-boggling abundance: fresh salads in December, carrots in February, spinach in March, and a whole new appreciation of what’s possible.

“Some people want to plant a garden and have it over with. But I’ve had more produce in fall than I’ve ever had in summer,” Visser says.

For Adam Montri, who, with his wife, Dru, and young daughter, Lydia, runs Ten Hens Farm in Bath, Michigan, the difference a high-tunnel hoop house made on their farm was the ability to reap an income year-round rather than just for the summer season.

In his job educating about hoop houses, a joint project of Michigan Food and Farming Systems and Michigan State University, Montri also noticed a less tangible, but infinitely richer, change.

“You always get a community growing around the farmers’ markets,” he says. “This makes that com-munity happen year-round.”

For many farmers in the upper two-thirds of North America, planting under cover – whether that cover is as minimal as compost-heated planting beds with floating row covers or as intricate as a 30-by-90- foot greenhouse erected over cherry trees – can alter an operation’s destiny and the farmer’s relationship with the land.

The Vissers became four-season gardeners when they moved from a higher elevation down to Longmont, a town outside Boulder, Colorado. Another daughter was selling her small, turn-of-the-century home with an extra-deep lot, and Rick had long craved the space, soil and less harsh climate. When remodelers came to make changes to the house and make his garage an art studio, he had them rework the yard as well – incorporating six raised beds, a mini-orchard and composting area, a cold frame and two sheds.

That cold frame is now Visser’s pride and joy, much more so than a small kit greenhouse he attached to the warm west side of one of the garden sheds. Between the two, he’s able to grow sturdy tomato seedlings that germinate in the home’s basement and produce a crop of low-growing vegetables that feed the couple through the entire winter. The cold frame’s low height – only 6 to 10 inches above the ground, with interior soil levels below that – is sufficient to keep his crops growing. And the operation is low maintenance: He props each pane of glass up with a notched 2-by-2 in the mornings and closes them at night.

Sure, you might say, that’s possible in Colorado, with 5,000-feet-plus elevations and 300-plus days of sunlight per year to warm crops in covered beds. But what about cloudy Michigan? The hills of Pennsylvania? Wind-scoured Oklahoma? Yes, oh, yes, and, absolutely, yes.

Coleman, who can truthfully be called one of this revolution’s leaders, farms year-round in Maine’s USDA Hardiness Zone 5, not exactly known for sunny winter days and with lows of 10 to 20 degrees below zero. Pennsylvania State University is a hotbed of hoop-house research. And in Oklahoma – a relatively balmy Zone 7 – interest in season extension has snowballed, says an agriculture foundation expert.

By selecting cold-hardy crops and varieties within those crops, by understanding the effect of well-timed and successive plantings to correspond with crucial day-length thresholds, and by using one or two levels of climate protection, the farm is able to produce market crops of superb quality and freshness 47 weeks of the year. (After assessing market demand, profitability and the need for some fallow time for themselves, they decided to set aside five weeks for a well-earned vacation.)

Four Seasons Farm, which Coleman operates with his wife, Barbara Damrosch, represents the opposite end of the complexity and size spectrum from the Vissers’ home garden. The farm sells a variety of fieldgrown vegetables throughout the warmer months, but is able to get an extra-early start with heat-loving crops, such as tomatoes, using a combination of a seed-starting greenhouse and a minimally heated “cool house” that becomes warmer as summer nears.

Key to the farm’s other-than-summer sales are four other structures: moveable, unheated greenhouses in which cold-hardy crops are grown in the soil and under a secondary, spunbond cover about 12 inches above the soil. Radishes, lettuce, mache, and a “stir-fry pack” of pak choi, carrot, radish, leek and “Hakurei” turnip with greens not only grow well in these cool conditions, he writes, they have excellent eating quality. If you visit them at the night’s lowest temperature, he says, the plants look as though they’ll die from frost by morning – but once the sun is truly up, they’re alive, vibrant and growing.

“The winter harvest would appear to have endless potential for all of us involved in exploring it. We are just beginning to tease out the possibilities,” Coleman writes.

There are winter-conquering strategies between the two extremes of cold frames and high-tunnel hoop houses. Jeff Ashton’s book came about because he was an inveterate tinkerer.

“It’s in a guy’s nature to try to reinvent the wheel. And I was obsessed with gardening, so I read everything I could get my hands on. I read the current stuff, and then I went backwards. In the past, gardeners have had to come up with strategies to grow things fresh, out of season, if they wanted to have them.”

At that time, Ashton’s roots were planted in Asheville, North Carolina, where cold, humid winds can tumble down the mountains, sometimes bringing snow. He gradually decided to grow all of his seedlings in his cold frame. “They come up slower, but they come up stronger, and they’re already hardened off. Less is more – and less work is definitely more.” His lesswork techniques for smaller-scale gardens include lampshade-frame, paper cloches, low hoops and row covers.

Ashton’s 2001 manual, now out of print, harbors construction-guy plans and detailed hardware recommendations for cold frames, low tunnels, “stoop houses,” and larger, but still small-scale, economical structures. He reminds gardeners to use such techniques to extend the harvest season, not to try to grow vegetables that are radically out of season. Tomatoes in April? No. But overwintered carrots and salsify roots? Yes. Kale, parsnips, brussels sprouts planted in summer, and harvested throughout winter? Absolutely, deliciously yes.