Many gardeners grow extra vegetables and fruits for winter storage, but how can you make your produce store for the longest time possible? First, remember that good produce storage quality begins at harvest.
Avoid physical damage during harvest. Most fruits and vegetables are easily bruised if not handled carefully. When harvesting, treat produce as if it were fine china. Tossing fruits and vegetables into baskets or boxes may not leave visible bruises and damage, but decay will begin under the skin. Seemingly sturdy vegetables such as sweet potatoes are actually quite delicate and will not store well if bruised. Any damaged produce should be used as quickly as possible and not placed in winter storage.
Root crops such as beets, carrots, rutabagas, parsnips and turnips can be left in the garden into late fall and early winter. A heavy mulch of straw will help prevent the ground from freezing so the roots can be dug when needed. The mulch will also maintain the quality of the roots, as it will reduce repeated freezing and thawing. Many people prefer the taste of these root crops after they have been frosted because their flavors become sweeter and milder.
When temperatures drop low enough to freeze the ground under the mulch, finish harvesting the roots. Cut off all but one-half inch of the top and store at 32 to 40 degrees Fahrenheit in high humidity to reduce shriveling.
Not all produce should be washed after harvest, including onions, garlic, Irish potatoes and sweet potatoes.
Some produce, however, should be washed and dried before storing, including winter squash and pumpkins, along with green and red tomatoes. Commercial packinghouses use sanitizers in packing line water to kill the fungi, bacteria and yeast that might otherwise cause spoilage. Sodium hypochlorite (liquid laundry bleach, 5.25% concentration) is the most readily available of these sanitizers for home gardeners.
Cool produce before washing, then use water a few degrees warmer than the fruits and vegetables to mix up your solution. This prevents cold wash water from being pulled inside the fruits along with any pathogens in the wash water. Dip produce in a solution of 1 ½ teaspoons of liquid bleach added to each gallon of warm wash water. Do not allow produce to sit in water; a quick dip is sufficient to remove pathogens.
Several vegetables benefit from post-harvest curing. Curing heals or suberizes injuries from harvesting operations. It thickens the skin, reducing moisture loss and affording better protection against insect and microbial invasion. Curing is usually accomplished at an elevated storage temperature and high humidity.
Produce can be cured in home storage areas. Temperature and humidity should be managed as accurately as possible. A space heater in an enclosed area can provide the needed heat for curing. Humidity can be increased by overlaying containers with sheets of plastic.
For specific guidelines on curing garden produce, refer to NebGuide G1264 Storing Fresh Fruits and Vegetables.
Storing Garden Produce
Proper long-term storage of homegrown vegetables and fruits depends primarily on two factors: air temperature in the storage area and humidity levels. Different vegetables or fruits have different storage requirements, although three main storage regimens predominate, including 1) Cool and dry, 2) Cold and dry, and 3) Cold and moist.
Cool and dry storage consists of 50-60° F temperatures and 60% relative humidity. In the home, basements are generally cool and dry making this the easiest storage regimen to achieve. However, in the winter with a furnace and dehumidifier running, the humidity may drop below optimum. If storing vegetables in basements, provide them with some ventilation. Harvested vegetables still "breathe" and require oxygen to maintain high quality. Also, be sure they are protected from rodents. Cool, dry storage is ideal for winter squash and pumpkins.
Cold and dry storage is 32-40° F temperatures and 65% relative humidity. For cold storage items 32° F is ideal, but is difficult to achieve in the home. For every degree above 32° F, expect a shorter storage life of your produce, as much as 25% for every 10°F increase in temperature. Refrigerator conditions are generally cold and dry, so an extra refrigerator is fine for long term storage of garlic and onions.
Cold and moist storage consists of 32-40° F temperatures and 95% humidity. Root cellars provide cold and moist conditions, or try refrigerator storage with the produce in perforated plastic bags. Produce can be placed in perforated plastic bags to increase humidity, however, unperforated plastic bags may result in water condensation inside the bag that leads to the growth of mold and bacteria. Make sure the produce has adequate ventilation or air movement, and if using a root cellar, protect it from rodents. Clean straw, hay and wood shavings may be used for insulation. Cold and moist conditions are best for the storage of beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, kohlrabi, parsnips, radishes, rutabagas and turnips.
Apples and pears also store best under cold (30-32° F) and moist (90% humidity) conditions, however, it is best to store apples separately because they give off ethylene gas which speeds the ripening of other produce.
For specific information on the ideal conditions for many common fruits and vegetables, refer to NebGuide G1264 Storing Fresh Fruits and Vegetables.
Preparing Onions for Winter Storage
One specific example of storage of a vegetable is onions. These can be harvested when the tops have fallen over and begun to dry. Do not bend over the tops during the growing season to force the energy into the bulb. This practice reduces the growth of the onions as they will not be able to translocate sugars to the bulb for storage.
Home gardeners should cure onions after harvest by spreading them in a single layer on screens in the shade or in a well-ventilated garage or shed for one to two weeks or until the tops are completely dry and shriveled. If the bulbs are exposed to full sun, prevent sunscald by allowing their foliage to cover them or by covering them with a light-weight cloth. When the tops are dry, they should be trimmed to one-inch lengths. Leave the onions dry outer skins on; they help reduce bruising and shrinking and act as an insect barrier.
Store onions in shallow boxes, mesh bags or hang them in old nylons in a cold, dry well-ventilated room. The tops may be left untrimmed and braided together. Temperatures close to 32 degrees F. will give the longest storage. Products prone to absorb odors or flavors should not be stored close to onions.