Onions should be harvested when most of the tops have fallen over and begun to dry. Carefully pull or dig the bulbs with the tops attached.
After harvesting, dry or cure the onions in a warm, dry, well-ventilated location, such as a shed or garage. Cure the onions for 2 to 4 weeks until the onion tops and necks are thoroughly dry and the outer bulb scales begin to rustle. After the onions are properly cured, cut off the tops about 1 inch above the bulbs. As the onions are topped, discard any that show signs of decay. Use the thicknecked bulbs immediately as they don't store well. An alternate preparation method is to leave the onion tops untrimmed and braid the foliage together.
Place the cured onions in a mesh bag, old nylon stocking, wire basket, or crate and store them in a cool, dry location. Storage temperatures should be 32 to 40 F. Possible storage locations include a basement, unused bedroom, or unheated garage. Since the temperature in an unheated garage may fall well below 32 F, an alternate storage site will be needed when bitterly cold weather arrives.
The storage life of onions is determined by the variety and storage conditions. Good keepers, such as Sweet Sandwich, that are properly stored should keep for several months. Onions will sprout if the storage temperatures are too warm. Rotting may be a problem in damp locations.
This article originally appeared in the August 27, 1999 issue, p. 115.