A root cellar is an underground or partially underground storage space that uses the earth's natural thermal mass and humidity to preserve vegetables, fruits, and preserved foods. Root cellars maintain temperatures of 0 to 10 degrees Celsius (32 to 50 degrees Fahrenheit) and humidity levels of 85 to 95 percent, conditions that slow respiration and spoilage in stored produce. A well-designed root cellar can keep root vegetables, winter squash, and apples fresh for 4 to 8 months without refrigeration.
Underground cellars are completely buried, with an entrance via a hatch or stairwell. These provide the most stable temperatures and are ideal for cold climates. The earth cover should be at least 60 centimeters (24 inches) for frost protection. Hillside cellars are dug into a slope, providing natural drainage and easy access at ground level. These are the most common type on homesteads with sloping terrain.
Above-ground cellars use thick insulation and thermal mass to simulate underground conditions. A northern-facing room with heavily insulated walls, a Concrete Foundation floor, and a small high window can function as a root cellar. These are less temperature-stable but can be retrofitted into existing buildings.
Basement root cellars are created by partitioning off a corner of an unheated basement, preferably on the north side. The enclosed space is insulated from the heated portion of the basement and vented to the outside for cold air intake.
Ventilation is critical for removing ethylene gas produced by apples and pears, which accelerates ripening and spoilage of other produce. An intake vent near the floor and an exhaust vent near the ceiling, both screened against rodents, provide natural air circulation. The vents should be closable to regulate temperature during extreme cold. Shelving is constructed from wood or metal, with slatted shelves to allow air circulation. Produce is stored in single layers on shelves or in bins filled with damp sand or sawdust.