Onions are a hardy vegetable that grow best in cool weather. When planting onions, you have 3 options–seeds, sets, and transplants.
Start seeds indoors 10 weeks before the frost date, but I suggest purchasing sets or transplants.
Plant onion sets outside as soon as you can work the soil, about 8 weeks before the frost date. These look like dry mini-onions. Plant them pointy side up. The smallest sets can be planted every 4-6″ (4 or 9 per square foot) to grow into mature onions. Plant the bigger onion sets every 3″ (16 per square) to grow green onions.
For onion transplants, harden off and transplant outside 4 weeks before the frost date.
Onions can be planted in the fall only in frost-free areas.
Soil and Fertilizer
Onions grows best in a rich soil; amend with lots of compost and fertilizer (chemical or organic) at planting and twice during the season.
Harvest green onions anytime after they reach 6″. For mature and storage onions wait until about half the tops turn brown and fall over, then carefully bend the rest over and let them sit for a few more days. Pull them out and let them “cure” for at least a week to allow the outer skins to dry out. Store in a very cool (but not freezing), dry place.
Check out this fun way to store onions!
Similar to: leeks
- Onions Reference Sheet (Utah Extension Service)
- Fertilizing Onions
- Storing Onions
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