Answer: In warm regions (zones 8-10) you can plant onion sets in fall for spring harvest. In cold regions like yours, it's best to wait until spring to plant. Most onions require long days (where the number of hours of daylight exceeds the number of hours of darkness) to stimulate bulb formation--thus, the bulbs don't begin to form until late spring/early summer, growing to maturity by late summer or early fall. Short-day onions are suitable for growing only in warm regions, where they can mature in late winter/early spring.
You can, however, plant onion sets in mid-summer, and harvest the scallions, or green tops, during the fall.
Burpee sells onion sets only in the spring. Pinetree Garden Seeds (ph# 207-926-3400, web site: http://www.superseeds.com) sells Egyptian onions--these are perennials which are planted from sets in the fall. You can cut the greens through most of the winter, and in the spring lift some of the bulbs. In the second year, the plant produces small, elongated bulbs atop 3-foot stalks.
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