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Long-day onions need about 14Long-day onions need about 14 to 15 hours of daylight to bulb. In zone 7, you should grow short-day onions. The light in the South doesn't vary as much as the North.

2015 Special Edition Garden GuideCooking Fresh with The Old Farmer's AlmanacThe Almanac Monthly Digital MagazineWhat the heck is a Garden Hod?