Vegetable Storage in Root Cellars
HGA-00331 View this publication in PDF form to print or download.
In Alaska, cold winter temperatures and cold soils all year long make root cellars a good method for storing vegetables. Root cellars offer gardeners a method for storing produce through the winter or for holding produce until there is time for canning and freezing. Consumers can also use root cellars to store produce bought in bulk from the farmers market or grocery. High-quality, locally-grown vegetables can be available from the root cellar throughout the winter.
Stored fruits and vegetables are living organisms, and to keep the quality and nutritional value high, certain storage conditions should be met. The best conditions for each crop will vary, but the important requirements include temperature, moisture and ventilation. To have the best success using cold storage, select late-maturing varieties of vegetables that have been allowed to grow late into the fall and fully mature.
Temperature
During the day, plants make food through photosynthesis. At night or during storage, plants respire or use the stored food to survive and keep alive. To keep produce at the highest quality, it is important to slow down the growth and respiration with cool temperatures. Respiration reduces quality and speeds up with warmer temperatures. The optimum storage temperature for most vegetables is between 32° and 40°F. This temperature can be maintained by using insulation on walls and ceilings, thermostats and a heat source when needed. An adequate heat source can sometimes be as little as a 100-watt light bulb placed near the floor. Keep in mind that warm air rises and warmer temperatures will be found at the top of the root cellar. Thermometers can be positioned throughout the cellar to monitor temperatures.
Humidity
High humidity (between 80 and 95 percent relative humidity) keeps vegetables from drying out. The exception to this rule is with cucubits (squash family) and onions — vegetables that produce a thick wall. These vegetables prefer dry storage conditions and tend to mold when the moisture is high.
The easiest way to keep the moisture high is to have a dirt floor, which helps the root cellar keep a constant moisture during the winter. If the floor is concrete or wood, it may be necessary to place several pans of water on the floor. Vegetables are 90 percent water. The fuller the root cellar, the higher the humidity. That is why a small, full root cellar will work better than a larger one.
Ventilation
Ventilation is used to help control the temperature and humidity. Excess moisture that encourages mold can be exhausted and the room can be aired out when not in use. Be sure the ventilation system is screened to keep rodents out.
Harvest and storage
Choose to grow vegetable varieties that are late maturing or have good storing qualities. Harvest as late in the season as possible before a killing or damaging frost. Vegetables should be harvested in the morning after the dew has time to dry but before the afternoon heats up the vegetables. Remove the field heat by cooling in a cold place.
Produce can be grouped according to storage requirements into four groups: (1) cold and very moist, (2) cold and moist, (3) cool and dry, and (4) warm and dry.
Most vegetables need a cold and very moist storage condition because of thin skin or leaves. Thin skin produce, including beets, kohlrabi, turnips, carrots, parsnips, radishes and cucumbers, is harvested leaving a ½-inch stem and stored to retain moisture. This can be done with packing material or perforated plastic bags. Layer vegetables in packing materials such as moist sawdust, sand and peat moss.
Leafy vegetables such as celery, Chinese cabbage, endive, kale and cauliflower should be lifted out of the garden with roots attached and replanted in moist packing material. Vegetables with strong odors, such as cabbage and turnips, are best when individually wrapped in newspaper to prevent drying out and to reduce smells.
Potatoes and tomatoes need a cold, moist storage condition. Potatoes need to be cured in a warm environment before cold storage. Harvest potatoes late in the season and store in the dark at a warm temperature for 7 to 10 days to allow them to dry and develop thick skins. Then move them to a cold, dark area. If potatoes are stored together in crates or boxes, they will share moisture and keep each other from shriveling. Do not store potatoes above 40°F or they will begin to sprout.
Tomatoes are harvested leaving a short stem attached. Place tomatoes one layer deep in a shallow box and cover with newspaper to keep them from drying out.
Onions, like potatoes, are cured for several weeks after harvest. This allows the skin to become papery and the roots to shrivel. Onions are best stored in a cool, dry location with good air circulation. Onions are often braided or put in a mesh bag and hung from the ceiling of the root cellar.
Winter squash and pumpkins are best stored in a dry, warm spot such as the corner of a room indoors. Cut as late as possible before a frost, leaving a 2-inch-long stem. The more mature, the thicker the skin and more resistant to decay and drying out the vegetables will be. If stored in a moist location, squash will quickly mold.
Building a root cellar
A root cellar should be cold, dark and damp and in a convenient location. It is easier to control
temperature and humidity in a small cellar. Most families can get by with an area 4 feet by 6 feet in size. The most convenient location may be a walled-off part of a basement or garage area with a window for ventilation. A common location in rural Alaska is in the floor of the kitchen. With an inside installation, be sure to put a vapor barrier towards the inside of the root cellar to protect the rest of the house from excess moisture and rot.
In both attached and separate structures select wood designed for direct burial for the walls and floor. Check with the supplier to be sure that the wood treatment is not toxic in this application. Uninsulated masonry walls will conduct the cool ground temperature into your root cellar and are very durable. Water drainage is important for keeping out surface water in the spring and during summer rains. Insulate above-ground walls to protect from cold temperatures in winter and warm temperatures in summer. Be aware that seasonal frost can extend over 4 feet deep seasonally into the soil. Keep this in mind and make sure that the insulation extends below the frost line.
Storage Time and Temperature for Some Vegetables Grown in Alaska
| Vegetables | Temp F. | % Humidity | Storage Time | Comments |
|---|---|---|---|---|
| Beets | 32° | 90-95 | 3 months | Leave 1-inch stem. |
| Brussels sprouts | 32° | 90-95 | 4 weeks | Wrap to avoid drying |
| Cabbage | 38° | 90-95 | 4 months | Late maturing varieties ** |
| Carrots | 32° | 90-95 | 5 months | Top leaving ¼-inch stem * |
| Cauliflower | 32° | 85-90 | 3 weeks | Wrap in leaves * |
| Celery | 32° | 90-95 | 4 months | Dig with roots *** |
| Chinese cabbage | 32° | 90-95 | 2 months | Dig with roots *** |
| Cucumbers | 50° | 85-90 | 3 weeks | Waxed or moist packing * |
| Kohlrabi | 38° | 90-95 | 3 months | Trim leaves * |
| Onions |
32° |
55-60 | 8 months | Dry for two weeks. |
| Parsnip | 32° | 90-95 | 6 months | Top leaving ¼-inch stem * |
| Potatoes | 38° | 85-90 | 8 months | Pack in boxes unwashed. |
| Squash | 60° | 55-60 | 3 months | Winter types, leave 2-inch stem |
| Tomatoes | 60° | 55-60 | 8 weeks | Single layer in covered boxes |
| Turnips | 38° | 90-95 | 3 months | Waxed or moist packing * |
| Small fruits | 32° | 85-90 | 7 days |
* Pack in moistened sawdust or sand.
** Wrap in clean newspaper.
*** Replant in moist sand.
Phillip Kaspari, Extension Faculty, Agriculture and Horticulture. Originally prepared by Ray Morgan, former Extension Community Development Agent.
Revised June 2020