It is possible to grow enough onions in the home garden to last the year. Onions are normally harvested in mid to late summer, but they do not need the lengthy preparation that other vegetables do prior to storage. Onions are stored in their raw state, not frozen or canned. Proper curing, or drying, is the surest way to ensure the onions have a long storage life, followed by proper storage practices after curing. Most bulbing onion varieties store well, but the best long-term storage varieties are usually marked on on the seed packet as such.
Spread the onion bulbs in a shaded area outdoors immediately after harvest. Leave them outdoors until late afternoon so their surfaces can dry. Bring them indoors before evening dew coats them.
Brush the excess soil from the bulbs, then spread them out on large screens. Place the screens in a warm, well-ventilated room for three weeks so the onions complete their curing.
Cut off the tops of the onions once they are done curing. Cut the tops, or dried leaves, down to a 2-inch length with a sharp knife.
Place the onions in a mesh sack or spread them out in a box filled with straw. Set in a 35 to 45 Fahrenheit, dry room, such as an unheated basement, garage or shed. Store for up to four months.