Answer: Although you planted the same type onion, the differences you reported are weather related. Onions prefer cool temperatures in their beginning growth and warmer temps as they near maturity.
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.
Plant each "set" 1" deep and space them 6-8" apart. Onions tend to push themselves up out of the ground as the bulb forms.
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