Start Your Onions Early
Sow onion seeds indoors 6-8 weeks before your last frost date in spring. For a summer harvest, plant sets (small bulbs) or transplants in the garden 3 weeks before the last frost date. In mild-winter regions, you can plant transplants in early winter for an early summer harvest.
Harvest Your Onions
About 8 weeks after planting, scallion tops should be 6-8 inches tall and ready for picking. You can harvest green onions any time after the bulb has formed. Mature onions should be ready for harvest in mid- to late summer, when the green tops start to turn brown and fall over. Then simply pull the onions from the ground.
Storage or Sweet?
You can choose from two types of regular onions. Sweet onions are flavorful, mild tasting, and good raw in salads or cooked. However, they don't last long in storage. Storage onions will last as long as 4 months, but have a more pungent taste and are best cooked.