A root cellar is a structure, usually underground or partially underground, used for storage of vegetables, fruits, nuts, or other foods. Its name reflects the traditional focus on root crops stored in an underground cellar, which is still often true, although a wide variety of foods can potentially be stored, for weeks to months, depending on the crop and the conditions, and the structure may not always be underground.
Root cellaring has been vitally important in various eras and places for winter food supply. Although present-day food distribution systems and refrigeration have rendered root cellars unnecessary for many people, they remain important for many people who value self-sufficiency, whether by economic necessity or by choice and for personal satisfaction. Thus they are popular among diverse audiences, including gardeners, organic farmers, DIY fans, homesteaders, preppers, subsistence farmers, and enthusiasts of local food, slow food, heirloom plants, and traditional culture.
Root cellars are for keeping food supplies at controlled temperatures and steady humidity. Many crops keep longest just above freezing (1–3 °C) and at high humidity (90–95%), but the optimal temperature and humidity ranges vary by crop, and various crops keep well at temperatures further above near-freezing but below room temperature. A few crops even keep better in low humidity. Root cellars keep food from freezing during the winter and keep food cool during the summer to prevent spoilage. Typically, a variety of vegetables are placed in the root cellar in the autumn, after harvesting. A secondary use for the root cellar is as a place to store wine, beer, or other homemade alcoholic beverages.
Vegetables stored in the root cellar primarily consist of potatoes, turnips, and carrots. Other food supplies placed in the root cellar over the winter months include beets, onions, jarred preserves and jams, salt meat, salt turbot, salt herring, winter squash, and cabbage. A potato cellar is sometimes called a potato barn or potato house.
Separate cellars are occasionally used for storing fruits, such as apples. Apples are one of the crops that give off enough ethylene gas to hasten the overripening or spoilage of other crops stored nearby, although this effect is variable and many farms successfully store vegetables without segregating their apples. Water, bread, butter, milk, and cream are sometimes stored in the root cellar also. In addition, items such as salad greens, fresh meat, and jam pies are kept in the root cellar early in the day to keep cool until they are needed for supper.
The ability of some vegetables and fruit to keep for months in favorable cellar conditions stems in part from the fact that they are not entirely inanimate even after picking. Although they may no longer qualify as living, the plant cells continue to respire in some impaired but nonzero way, resisting bacterial decomposition for a time. The effect can be compared to the way that cut flowers in a vase of water last much longer than cut flowers lying on a table: the flowers in the vase are not entirely dead yet and continue to respire. The analogy is not exact, but the high humidity that supports many cellared crops is involved in this residual respiration.
In some cases plants are transplanted from the field to the dirt floor of a cellar in autumn, and they then continue living in the cellar for months. The fact that they cannot thrive or grow larger in the low-light, low-temperature conditions is not a problem; the only objective is to keep them alive instead of dead, thus warding off decomposition. This is a form of season extension in which the growing season is not extended but the harvest season is substantially extended.
Closets, crawlspaces, garages, sheds, and attics have all been used successfully for storage of at least some kinds of crops. Even the space under a bed can store some crops (such as pumpkins) for several weeks. Especially before rural electrification, farms with springhouses have often used them for root cellar duty (as well as milkhouse duty).
Common construction methods are:
- Digging down into the ground and erecting a shed or house over the cellar (access is via a trap door in the shed).
- Digging into the side of a hill (easier to excavate and facilitates water drainage).
- Building a structure at ground level and piling rocks, earth, and/or sod around and over it. This may be easier to build on rocky terrain where excavation is difficult.
- Bubel, Nancy; Bubel, Mike (1991), Root Cellaring: Natural Cold Storage of Fruits and Vegetables, ISBN 978-0882667034, OCLC 40137781.