Most onion varieties begin to form a bulb when the temperature and the number of daylight hours reach certain levels. Varieties listed as short-day onions bulb up when the day length is 11 to 12 hours. On the other hand, long-day onions begin to form a bulb when the day length is a minimum of 14 hours.
Keep in mind that the larger and sweeter cultivars, such as Spanish and Bermuda onions, don’t tend to store as well as sharp-tasting ones with smaller necks.
Northern gardeners should plant long-day onions. In the North, daylight length varies greatly as you get farther and farther away from the equator. Winter days are very short, but summer days are long. Long-day onions will have a chance to produce lots of top growth (hence produce bigger bulbs) before the day length triggers bulbing. If short-day onions were grown in the North, the onions would bulb up too early and
they would be small by comparison.
Southern gardeners should plant short-day onions. In the South, there is much less variation in day length between seasons than up North. If long-day onions were planted in the South, they may not experience enough day length to trigger the bulbing process.
Onions are sensitive to day length, so varieties are generally classified into three categories: Long-day, short-day, and day-neutral. The border between long- and short-day varieties lies roughly at 36 degrees north latitude (aka, the 36th parallel)—north of this line, plant long-day varieties; south of it, plant short-day varieties. Day-neutral varieties can be grown successfully anywhere.
- Yellow Sweet Spanish Utah: large, globe shape; yellow-white
- Gabriella: jumbo bulbs, storage onion for short term
- Walla Walla: sweet onion with a short storage period
- Yellow Granex PRR: large yellow, flattened globe-shaped onions, crisp and sweet
- Yellow of Parma: yellow, flattened globe-shaped onions, crisp and sweet, incredibly long storage time
- Ringmaster: An improved variety of ‘White Sweet Spanish’, ‘Ringmaster’ is a white, long day, storage onion.
- Sturon: Medium, round brown globes have sweet yellow flesh, stores well
- Texas Supersweet: jumbo yellow-skin globes
- White Bermuda: extremely mild, with thick, flat bulbs; white
- Red Burgundy: good table onion with mild, sweet white flesh,& red-skinned
- Cippolini Red: small, flattened, disc-shaped bulbs, doesn’t store well
- Hybrid Yellow Granex: exceptionally sweet, mild onion made famous in Vidalia, Georgia, and Maui, Hawaii, and it stores well too.
- Texas 1015-Y Supersweet: stores very well
- Candy: golden, thick flesh; jumbo bulbs; stores well
- Red Candy: sweet, mild, red onion
- Red Stockton: large, red-ringed, white-flesh bulbs
- Super Star: large, sweet, white bulbs
“In the onion is the hope of universal brotherhood; if everyone will eat onions at all times, they will comme into a universal sympathy.” ~ Charles Dudley Warner