Fresh salads are what many gardeners want most in winter. It seems an impossible task in cold-winter regions, where snow and frigid temperatures are common. Even in the mildest regions, where it is much easier to grow a range of salad crops through the winter, many gardeners unnecessarily let their gardens go fallow. But no matter where you live, according to Eliot Coleman of coastal Maine, a cold frame or tunnel greenhouse can put just-picked salads on the table through the coldest months.
Coleman discovered the secret to abundant winter harvests when he realized that the plants don't have to actually grow in winter. They only have to stay alive. The growing is done in late summer and autumn. Get the salad crops to edible size before serious cold arrives, then the frame can serve as an oversized crisper drawer through the dead of winter. A simple cold frame can do that for a wide range of salad crops.
The greens that I harvest in winter are plants that can stand freezing at night but then regain their firm, crisp texture when they thaw the next day. Lettuce doesn't take repeated freezing well, but arugula, claytonia, mache and mizuna do very well," notes Coleman. "We enjoy fresh salads all through January and February, from crops sown in August, September and October."
Coleman recommends one four- by eight-foot cold frame per person. A frame that size, full of well-grown salad crops at the start of winter weather, should provide enough salad for one person to pick every day.
The soil in frames should not be excessively rich. Coleman recommends one to two inches of high-quality compost worked lightly into the top inch of soil at the start of the season. No liquid fertilizers of any kind are needed. And once the frames are closed up, little watering is required, depending on the intensity of the sunlight.
The frames do need to be vented regularly, however. And if the gardener will be away during the day, it is better to err on the side of too cold than too warm. So open the frames if the weather is bright and the frames might get warmer than 70oF. Remember, the crops for the most part are already grown, and all are plants that can tolerate light freezing, in case the weather should change.
"Trying for an all-winter salad supply might sound like a chore," says Coleman. "But it becomes a small and comfortingly regular task, like gathering the mail or shopping for food. It is not at all unpleasant. I suggest that you try with one small bed, and see what you can do. You should get salads once a week or every other day. You may even find that you can get them every day like I do. These fresh salads may not seem like much at first but, I assure you, they will become one of the greatest pleasures your garden provides."
Recently, arugula has become king of gourmet salad greens. It's also among the hardiest. The plant achieves finest flavor when grown in the cooler months, and the leaves maintain quality through repeated freeze/thaw cycles.
Coleman harvests October-sown arugula in his tunnel-covered cold frames through January. For midwinter, the variety Selvatica takes the cold a little better and is a little milder flavored, though it's a bit slower to germinate tha the ordinary arugula.
"Arugula is what I find myself sowing the most. It's quicker to sprout and grow over a wider range of temperatures than just about anything else. In January, when I stop strewing mache in gaps between plants, I start with the arugula seed," he says. Thinnings from early January are big enough to harvest in two months.
Plant arugula in rows four inches apart, with seed about an inch apart in the row. Begin harvesting plants at two inches tall, until plants are six inches apart. Cut the tough root. On larger plants, harvest outer leaves.
This is the Pacific Coast miner's lettuce, which has been selected for winter salad production by German and Dutch seedsmen. In Europe it's sometimes called winter purslane. The plant produces a cluster of smooth, tender leaves atop four-inch stalks that arise from a crown that will produce new leaves all winter. In spring, clusters of white flowers form where the stalk joins the leaf. The leaves with flowers are edible, too -- it's one of the few leaf crops whose flavor doesn't go downhill when the plant begins to flower.
Coleman broadcasts the very small seed in shallow rows spaced four to six inches apart. In the furrows, the seed should be about an inch apart. Begin harvesting two months later. Coleman grasps a bunch of the leaf stalks and cuts them about four inches below the leaf. Then he trims off the bottom two inches for the compost pile. The plant grows a new cluster of leaves and the harvest continues in the frames all winter.
Both ragged-edged and the broad-leaved (or escarole) endive make very large plants, much bigger than a lettuce. Late in the season, once plants are large, tie leaves into a bunch to make a blanched heart. Protected by frames, these will last well into winter. Though the outer leaves freeze and spoil, there will be a delectable heart inside even in January.
To get large endives takes about 80 days, but some smaller types mature more quickly, and any will give delicious, "thinning"-sized plants (about four inches tall) in 45 days. In the North, a September sowing will not make large heads. In the South, sow endive thick and early for thinnings and for large heads in winter. Small endive plants are a component of mesclun, a mixture of young salad greens. Younger leaves are more delicate and not as strong-tasting as mature leaves. In frames, sow the seed an inch apart and harvest thinnings. Once the plants are about six inches apart, begin harvesting outer leaves.
In Coleman's climate, lettuce is a fall salad staple and is not reliable for winter harvest. Quality declines rapidly when leaves begin to freeze and thaw. Coleman's lettuce is finished the second week in December, even with the double protection of cold frames and tunnels. In milder climates, lettuce can star in salads all winter.
For fall harvests, any lettuce works well, but butterhead types best withstand extreme cold. Sow in containers every two weeks from early August to mid-September. Transplant to outdoor beds or frames when plants are two inches tall. Harvest from October through November.
Late in September, Coleman sows lettuce that will winter over in the frames as small plants and become the first lettuce crop in spring. He transplants when the plants reach about two inches across, at a six- by six-inch spacing.
Also known as field salad or corn salad, mache is the only plant that actually keeps growing all winter, and it is Coleman's midwinter salad staple. Even -20° F won't hurt it. Harvest whenever frames warm enough to thaw leaves.
Mache has bright green, thumbnail-sized leaves that grow in a rosette that reaches three inches across at harvestable size. The texture is buttery and soft, the flavor mild. Cut the plants just above soil level, leaving roots in the ground. Whole rosettes go into salad; one plant makes a forkful.
Mache won't germinate in warm soil. Coleman plants in frames in early September, sowing the seed into shallow drills about four inches apart and covering the seed lightly. Make seed rows an inch or two apart. You don't want to have to thin m'che, he says: Pulling it by the roots will scatter soil on nearby leaves. Whenever space appears in the frames, Coleman advises scattering more seed. He sows seed through the middle of December, so there's always more maturing somewhere. M'che planted outdoors is allowed to grow on through the winter for harvest the following spring.
Even though mizuna is related to Chinese cabbage, it looks more like a very frilly form of endive. The plants have many slender leaves arranged in a thick, flattish head. The leaves are long and thin, and very finely cut. Another form has leaves that are spoon-shaped at the tips, not frilly. The flavor, however, is much milder than other Chinese cabbages or endive. Mizuna is a superb winter salad vegetable.
Coleman sows it in the late summer and early autumn, then harvests whole plants like young endive, at the thinning size -- three to four inches tall. When the plants are about six inches apart, he begins harvesting the outer leaves. Autumn plantings will yield through winter. If mizuna seed is scattered in empty spots in the frames in late January, thinnings will be ready for salads late in February.
The buttery, soft leaves of spinach go much further in the salad bowl than they do in the pot. The plant will germinate and grow at temperatures in the 40° Fs. Coleman's favorite variety for winter is 'Tyee', but he says that 'Indian Summer' and 'Winter Bloomsdale' are almost as good.
Two weeks before first frost, Coleman begins to plant spinach in frames for late fall harvests. The planting in frames can continue for the next four weeks. In frames that are later covered with tunnels, the spinach harest can continue all winter. Spinach planted outdoors at the same time, then covered with mulch when the temperature approaches 20? F, will survive the winter and yield the earliest possible crops. A couple of weeks after frost, he'll plant more in frames outside the tunnel. That sowing won't get big enough to harvest for winter salads, but will winter over and produce an extra-early crop as winter ends.
By adding a polyethylene-covered tunnel over his cold frames, Coleman figures he has moved his winter garden two or three zones south, varying with the severity of his zone 5 winter. In places with mild winters, tunnels are dry and pleasant places to garden all winter, and thus may be preferable to frames.
Eliot Coleman builds and uses cold frames artfully. His frames are four feet long and eight feet wide.
Here are ways to make and manage a cold frame in your garden:
Jack Ruttle is a former editor at National Gardening.
Photography by National Gardening Association and Suzanne DeJohn/National Gardening Association
Article published on June 23, 2008.