The following is an excerpt from Four-Season Harvest: Organic Vegetables From Your Home Garden All Year Long by Eliot Coleman. It has been adapted for the Web.
No one wants second best. A slimy cabbage from a dingy corner of the basement will never compete with the crisp specimens on the vegetable shelf of the supermarket. Wilted, dried-out carrots look unappealing next to the crunchy, plastic-wrapped beauties in the refrigerator. When home storage is unsuccessful, a case can be made for artificial refrigeration. But the cabbage need not be slimy nor the carrots wilted. A properly constructed root cellar does not take a backseat to any other method of food storage. It is no great feat to manage a simple underground root cellar so that the produce will be equal or superior in quality to anything stored in an artificially refrigerated unit, even after long periods of storage.
A successful root cellar should be properly located, structurally sound, weather tight, convenient to fill and empty, easy to check on and clean, and secure against rodents. Proper location means underground at a sufficient depth so frost won't penetrate. The cellar should be structurally sound so it won't collapse on you. It needs to be weather tight so cold winds can't blow in and freeze the produce. You need to have easy access to fill it, to use the produce, and to clean it at the end of the winter. And it should be rodent-proof so all the food you have stored away won't be nibbled by rats and mice.
Provision must be made for drainage as with any other cellar, and the cellar should be insulated so that it can maintain a low temperature for as long as possible and provide properly humid storage conditions. Finally, microclimates within the cellar (colder near the floor, warmer near the ceiling) should allow you to meet different temperature and moisture requirements for different crops. The cellar will be most successful if it incorporates your underground food storage needs into one efficient, compact unit. It's surprising how easily a hole in the ground meets all those conditions.
Any house with a basement already has a potential root cellar. You just need to open a vent so cold air can flow in on fall nights, and sprinkle water on the floor for moisture. The temperature control in the root cellar is almost automatic because cold air, which is heavier than warm air, will flow down, displacing the warmer air, which rises and exits. This lowers the temperature in the cellar incrementally as fall progresses and the nights get cooler. By the time outdoor conditions are cold enough to require moving root crops to the cellar (around October 21 to November 7 here in Maine), conditions in the underground garden are just right-cool and moist. With minimal attention, they will stay that way until late the next spring.
No wood or other material that might suffer from being wet should be used in root cellar construction. The ideal root cellar is made of concrete or stone with rigid insulation around the outside. Any permanent wood in a root cellar soon becomes damp and moldy. Wood will not only rot but also will serve as a home for bacteria and spoilage organisms and is subject to the gnawing entry of rodents. The stone or concrete cellar is impregnable. It won't rot or decompose, and the thick walls hold the cool of the earth.
The easiest way to make a root cellar is to wall off one corner of the basement as a separate room. The best material is concrete block. There is no problem even if the rest of the basement is heated. You simply need to insulate one temperature zone from the other. Leave enough space between the top of the walls and the joists of the floor above so you can install a cement-board ceiling with rigid insulation above it. Also attach rigid insulation to the heated side of the cellar walls you build. The insulation can be protected with a concrete-like covering such as Block Bond. Install an insulated metal door for access, and the structure is complete.
There are several simpler options, especially for storing small quantities of vegetables. If your house has an old-fashioned cellar with a dirt floor and there is enough drainage below floor level, you can dig a pit in the floor 18 to 24 inches deep, line it with concrete blocks, and add an insulated cover. You will want to open the cover every few days to encourage air exchange in the pit. The pit won't be as easy to use as a room you can walk into, but like any hole in the ground, it should keep root crops cool and moist. In warmer climates, you can use similar pits or buried barrels for storage either outdoors or in an unheated shed.
One of the simplest techniques we ever used, before we had a root cellar, was to dig pits in one section of the winter greenhouse. In that case we used metal garbage cans and buried them to their edge in the soil under the inner layer. To make sure they stayed cool we insulated their lids. We filled those cans with all the traditional root crops after their late fall harvest. Our whole winter food supply that year was in one central spot and when we went out to harvest fresh spinach and scallions for dinner we would bring back stored potatoes and cabbage at the same time.
"The winter was not given to us for no purpose. We must thaw its cold with our genialness. We are tasked to find out and appropriate all the nutriment it yields. If it is a cold and hard season, its fruit, no doubt, is the more concentrated and nutty."
—Henry David Thoreau
PRESENTING THE FOUR-SEASON HARVEST
A heavy wet snow is falling today. There could be a foot or more, said the radio, before its voice was silenced by a toppling tree that took out our power. It's a beautiful snow, clumping thickly on the evergreen woods that encircle our little house and bringing them in closer like a soft white duvet. This is the fourth snowfall so far this month, and it's the 10th of April. Being vegetable gardeners of great enthusiasm you would think we'd be dismayed, champing at the bit, eager to grow fresh food for the table again. But that is all in the past. We have managed to turn winter from deprivation to celebration.
We throw on our coats and go out to the cold frames to pick a salad for dinner. The cold frames are glass-covered, bottomless wooden boxes, eight feet long and four feet wide, lined up at the back of the garden along our gravel path, and a celebratory sight they are as full of green bounty as the produce aisle at the local market. Lifting up the glass lids and propping them with a notched stick, we are treated to a good whiff of moist unfrozen soil. While the snow sifts about us we get busy cutting tender leaves with small serrated knives, filling a towel-lined basket. Dressed with a good olive oil and a squirt of lemon, the salad will taste like renewal—a perfect accompaniment to the leek and potato soup simmering on the back of the stove.
This fresh daily harvest goes on all year, both from our traditional outdoor summer garden and our unconventional protected winter garden. The results are sumptuous. Dinner guests habitually exclaim about the freshness and flavor of our salads and always ask,"What all is in there?" In January, for example, our answer might be "a mix of frisée endive, baby leaf spinach, Chioggia radicchio, wild arugula, miner's lettuce, buckshorn plantain, and corn salad." We can almost anticipate the next question.
"From where?" they query; slightly conspiratorially, expecting us to confess to expensive overnight air delivery from exotic foreign suppliers. When we tell them we harvested the salad earlier that day from our unheated winter garden, the suspicion changes to stunned disbelief. "In winter? But it's too cold."
"Not for these crops. They don't mind freezing temperatures. These greens are the traditional winter peasant foods of southern France and northern Italy. Granted our winters are colder, but our simple protection makes up for the lower temperatures.
They nod in understanding but then pause again after a few more mouthfuls."But you don't have enough sun way up here, do you? I mean, southern France is like Florida."
We acknowledge it may seem like that is so, but the truth is something different. "Based on daylength and sunshine, Miami, on the 26th parallel of latitude in Florida, corresponds with the city of Luxor, near the ruins of ancient Thebes, on the shore of the Nile River in southern Egypt. In contrast, the resort town of Cannes on the Mediterranean coast of France has the same winter sunshine and daylength as the city of Portland on the Atlantic coast of Maine."
"Maine? I can't believe it."
"It's true. Most of Europe lies further north on the globe than the U.S. does. Our farm on the 44th parallel in Maine is on the same latitude as Avignon in southern France and Genoa on the warm Ligurian coast of Italy. That means we have the same daylength and amount of sun they do."
The visitors' surprise and their response are not unexpected. We have received that same reaction from gardeners everywhere. In the first place, many people assume all vegetables will be killed by freezing temperatures in winter. Yet we habitually grow some thirty different crops that survive freezing temperatures with no problem when given a little protection from the wind, which is the real outdoor plant killer in winter. Secondly, many people assume there will not be enough sunshine during the winter months. Yet we get as much sunshine as regions of the world where winter gardening is traditional. That latter fact is probably the most surprising.
It is logical to assume that warm temperatures and sunshine go hand in hand. If France has a warmer winter climate, it must be sunnier. In truth, since Avignon has more cloudy winter days than we do, there is actually more winter sunshine in Maine. That raises an obvious question. Then how come the Maine climate and the French climate are so different? Just because we are on the same latitude doesn't necessarily mean we have the same climate. The climate difference between southern France and mid-coastal Maine is caused by forces independent of latitude. Different climates are a result of different air and ocean currents.
Whereas masses of cold arctic air moving south across Canada give the northern parts of the North American continent a mostly frozen winter, the situation in France is different. The Gulf Stream, a massive flow of warm water moving northward across the Atlantic Ocean from the Caribbean to Scandinavia, ensures that western Europe's winter will be mostly cool and moist. Similarly, the warm Pacific currents on the west coast of the U.S. mean that Juneau, Alaska at latitude 570 has a warmer average temperature in January than New York City at latitude 41º. If judged on temperature alone, a gardener in Juneau should have a slightly easier time growing winter vegetables than a gardener in New York. But for winter vegetable crops, temperature is not the principal deciding factor. Daylength—the amount of available sunlight—is.
And that brings us back to latitude. Latitude determines daylength and the quantity of potential sunlight available to a winter gardener. Places around the globe at the same latitude will have the same daylength. Thus our Maine farm in the northeastern corner of the U.S. shares a "sun line" with those parts of France, previously mentioned, which lie on the same 44th parallel. Places to the north of that line, such as the rest of northern Europe, have less winter gardening potential than we do. And places to the south of that line, which includes 85 percent of the U.S., have better sun for winter vegetable gardening than Mediterranean France. We should make better use of it.