Root cellars provide a cool and dark environment that extends the shelf life of produce such as apples, pears, potatoes, carrots and turnips. By taking advantage of nature’s cold storage facility instead of purchasing frozen and canned goods from grocery stores that have often traveled thousands of miles before reaching you home, keeping the proper temperature and humidity conditions is critical to keeping these vegetables at their freshest.
Temperature
Root crops flourish at temperatures between 32-40 degrees Fahrenheit. Cool temperatures slow the ripening process and decomposition of crops; too hot a temperature could ruin them while too low may dry them out prematurely.
Humidity An optimal humidity range in a root cellar should range between 85-95% to prevent vegetables from drying out and molding, and also help stop botrytis cinerea from appearing on surface vegetables.
To achieve high humidity levels in a cellar, it should either be underground or built of insulated walls. A cellar on a concrete slab could benefit from being lined with sand or sawdust to reduce air drying out too quickly; while for non-ground cellars an air humidifying box filled with sand, moss, or straw may provide enough humidity for optimal conditions.
Ventilation Root cellars need plenty of ventilation, which can be achieved either by opening windows during winter and spring or using a hygrometer to monitor relative humidity levels in the cellar. Proper ventilation prevents mold growth from developing while dispersing any ethylene gas produced by fruits and vegetables into other parts of the cellar so it does not impact their quality.
Root cellars typically are constructed underground as the earth acts as a passive insulator and temperature regulation is easily managed with soil amendment. But if digging down isn’t an option, The Bubels suggest building one from concrete or using an “insulated closet,” such as one located within your basement that has been partitioned off with walls for insulation purposes. Their book Stocking Up contains construction details for various underground and aboveground storage options including mound storage, pit storage, hay bale storage and earthen cellars.