Richard Jauron
Extension Horticulturist
515-294-3108
rjauron@iastate.edu
Onions are a staple in the kitchen. If properly harvested, cured and stored, homegrown onions can be enjoyed through much of fall and winter. For more information on onions or to ask other gardening questions, contact Iowa State University Extension and Outreach horticulture experts at hortline@iastate.edu.
When should onions be harvested?
Storage onions should be harvested when the tops have fallen over and turned brown. Most onion cultivars mature 90-120 days after planting. Carefully pull or dig the bulbs with the tops attached.
How should I dry and store onions?
After harvesting, dry or cure the onions in a warm, dry, well-ventilated location, such as a shed or garage. Spread out the onions in a single layer on a clean, dry surface. Cure the onions for two to three 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 thick-necked bulbs as soon as possible, as they don’t store well. An alternate preparation method is to leave the onion tops untrimmed and braid the dry foliage together.
Place the cured onions in a mesh bag, wire basket or crate. It’s important that the storage container allow air to circulate through the onions. Store the onions in a cool, moderately dry location. Storage temperatures should be 32-40 degrees Fahrenheit. The relative humidity should be 65-70%. Possible storage locations include a basement, cellar or garage. Hang the braided onions from a rafter or the ceiling. If storing the onions in an unheated garage, move the onions to an alternate storage site before temperatures drop below 32 F.
How long can onions be successfully stored?
The storage life of onions is determined by the cultivar and storage conditions. When properly stored, excellent storage onions, such as Copra, Redwing, Red Zeppelin and Stuttgarter, can be successfully stored for several months. Poor keepers, such as Walla Walla and Sweet Spanish, can only be stored for a few weeks.