Horticulturists with Iowa State University Extension and Outreach answer questions about growing onions.
The storage life of onions is determined by the variety and storage conditions. When properly stored, good keepers such as 'Copra' 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.
Onions are a staple in the kitchen. They’re also easy to grow. If properly harvested, cured, and stored, gardeners can enjoy homegrown onions through much of fall and winter.
Onions are easy to grow. They perform best in well-drained, slightly acidic, fertile soils in full sun. Heavy soils can be improved by incorporating organic matter, such as compost, into the soil. Onions require higher fertility levels than most other vegetables. Apply 1 to 2 pounds of an all-purpose garden fertilizer, such as 10-10-10, per 100 square feet and till into the soil prior to planting. Four to five weeks after planting, sidedress with additional fertilizer. Sprinkle 1 pound of an all-purpose garden fertilizer per 100 feet of row. Place the fertilizer in a narrow band about 2 to 3 inches from the base of the onion plants.