Produce that requires cool-to-cold moist surroundings can be stored outdoors in areas that are not prone to flooding. All outdoor storage has the disadvantage of being unaccessible sometimes and subject to damage by rodents and other vermin. A well-drained location is essential to prevent excessive accumulation of water.
Usually the produce must be insulated for protection from frost and fluctuating temperatures. Insulating materials commonly used are straw, hay, dry leaves, corn stalks, or wood shavings, and some soil. Be sure that the insulating materials used are not contaminated with pesticides.
It is possible to leave some root crops, such as carrots, turnips, and parsnips in the garden where they grew, for part or all of the winter. (See fig. 1.) After the ground begins to freeze in the late fall, cover the root crops with a foot or more of mulch-straw, hay, or dry leaves. Do not place mulch on warm soil because doing so will cause vegetables to decay rapidly. Wait until the ground is cold.
Produce can be difficult to dig out of the frozen ground, but it will not be adversely affected until the temperature around the roots drops to 25˚F or less. Carrots are damaged at about 25˚F, but parsnips can stand somewhat lower temperatures.
Parsnips, horseradish, and turnips actually improve in flavor by light freezing. At temperatures between 28˚F and 34˚F, the starch changes to sugar.
Other crops, such as beets, cabbage, Chinese cabbage, cauliflower, celery, endive, cos or romaine lettuce, kale, leeks, and onions can withstand the early light frosts and can be stored for several weeks under a heavy mulch.
Mounds or pits are a very economical way to store cabbage and root crops, such as carrots, beets, celeriac, kohlrabi, rutabagas, turnips, and winter radishes. (See fig. 2.)
Select a well-drained location, and cover the ground with an insulating mulch. Making a shallow excavation (from 6 to 10 inches deep) and placing the produce partly below the surface will ensure better frost protection, but it will also increase the danger of excess water. Place mulch over vegetables. A ditch around the storage perimeter will help remove surface water.
Vegetables keep very well in pits and mounds, but once these storage areas are opened all the produce should be removed. After it’s removed, the produce will keep for 1 or 2 weeks at most. It does not keep as long after removal from storage as will freshly harvested produce.
Root crops can be mixed, but should be separated with mulch to prevent cross-transfer of odors. (See “Separating Fruits and Vegetables,” ahead.)