Onion bulbs form based on the amount of daylight they get. Northern gardeners will succeed with long-day varieties; southerners need to go with short-day options. Everyone else, take your pick of the intermediates.
'Cippolini'. An Italian heirloom that produces buttonlike, yellow onions from 2 to 4 inches around.
'Copra'. A very sweet, yellow-skinned hybrid.
'Gladstone'. Oblong, 4- to 5-inch bulbs.
'Red Burgermaster'. A mildly sweet hybrid red onion.
'Southport'. Large, long-lasting heirloom that comes in both red and white varieties.
'Candy'. A "day-neutral" hybrid with very sweet, large, yellow-skinned bulbs.
'Redwing'. A deep red, very long-lasting hybrid.
'Rossa di Milano'. Slightly spicy, medium-size red onion.
'Super Star'. Another "day-neutral" that's white, sweet, and shorter-lived in storage.
'Valencia'. Large, heavy (nearly a pound!) yellow-skinned bulbs.
'Bermuda'. Sweet, white onion that keeps only for a couple of months.
'Texas Super Sweet'. Large, sweet yellow bulbs.
Onion sets are available at most garden centers. Plant and seed sources:
Dixondale Farms, Carrizo Springs, TX; 877-367-1015, dixondalefarms.com
Johnny's Selected Seeds, Winslow, ME; 877-564-6697, johnnyseeds.com
Steele Plant Company, Gleason, TN; 731-648-5476, sweetpotatoplant.com
Territorial Seed, Cottage Grove, OR; 800-626-0866, territorialseed.com