AMES, Iowa – Onions are a common part of garden crops across Iowa, but harvesting, drying and storing them can come with difficulties for the uninitiated. How can these issues be avoided?
ISU Extension and Outreach horticulturists can help answer questions about harvesting, storing and drying onions.
When should onions be harvested?
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.
How should you 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 one 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, old nylon stocking, 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 to 40 degrees Fahrenheit. The relative humidity should be 65 to 70 percent. Possible storage locations include a basement, cellar or garage. Hang the braided onions from a rafter or ceiling. If storing the onions in an unheated garage, move the onions to an alternate storage site before temperatures drop below 32 degrees Fahrenheit.
How long can onions be successfully stored?
The storage life of onions is determined by the cultivar and storage conditions. When properly stored, good keepers, such as ‘Copra,’ ‘Redwing,’ 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.