Answer: Onion, Allium cepa, is an edible bulb root native to central Asia and the Mediterranean region. There are many varieties, yellow, red, white, some good for storage, some not suitable for storage. They prefer cool temperatures in their beginning growth and warmer temps as they near maturity. Green onions can be harvested forty-five days from planting transplants or sets.
Long day onions require 13-16 hours of daylight, and should be planted in the northern regions which, because of the tilt of the earth, actually have longer days in the summer. Short-day onions require only 12 hours of daylight, and should be planted in the southern regions. Onions that grow well anywhere are considered day-neutral.
Here's a terrific website with detailed information on short-day, intermediate and long-day onions:
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