Long Day onions grow better in the North where summer days are long. Usually zones 6 thru 3 are included in the Long Day onion group. Onions form bulbs in response to day length. Long-day onions need about 14 to 15 hours of daylight to bulb.
The White Sweet Spanish Onion is a long-day variety that has a sweet flavor with very little of the sharpness that some other onions have.