Look over any town in the USA and you will see many garages, tool sheds, storage units and even swimming pools, but you are unlikely to find a single backyard root cellar, or even many people who are familiar with the term. Yet root cellaring seems to have been practiced in most times and places, and even, in a sense, by animals who bury their food. It is a zero-carbon, zero-electricity, low-cost way to keep roots and other foods over the winter, simply by using the planet as your refrigerator.
Root cellars can take many forms, but they all work on the basic principle that vegetables in the right conditions stay alive, so they do not spoil, but also do not continue to grow, ferment, seed, bolt or any other plant activity. Since the temperature underground changes little throughout the year, this usually means keeping them partially underground and well-insulated.
Perhaps the easiest things to root cellar are the roots the name implies – carrots, potatoes, parsnips, beetroot, celeriac, turnips and so on. Many vegetables and fruits can be stored, however -- krauts like cabbage, broccoli, cauliflower and kale; onions and their relatives leeks and garlic; fruit like apples and pears; herbs and even salad greens. Most of the vegetables come from late-season plantings, when the crops are ripening at the latest possible moment before they must be stored for winter.
You can keep potatoes or carrots in boxes of earth, sand or sawdust. You can make a fort out of straw bales, as a child might do with pillows, and keep food cool inside. You can poke two pegs in the ground at either end of a crop row, pull string taut between them, and wrap plastic over the rope to make a long small tent. Some people have buried broken refrigerators and used them to store food.
Many potatoes and other vegetables can be piled into mounds and covered with earth and straw. Mounds should not be dug where water puddles, and while some gardeners dig out a mound first, we who live in the Bog of Allen might fine it safer to simply start on the ground level. The triangular pile should probably not be more than a metre high, to avoid the weight of the higher vegetables squashing the lower ones. Some kind of ventilation – a column of straw, a pipe -- needs to be put through the middle of the stack. The pile of potatoes are covered first with a layer of straw – 15 to 30 centimetres -- and then a layer of earth about half as thick.
Other people have built more elaborate structures. One could, for example, dig a pit about a metre deep and a few metres across, lean two wooden walls against each other in the pit to make a triangle, nail them together, and cover the top with a thin layer of earth. The result is a root cellar with an insulating earth and grass roof that can be a walk-in refrigerator during the winter months.