Growing Onions: Planting, Growing, and Harvesting Onions

Onions are “photoperiodic,” meaning they grow in response to day length—the number of daylight hours needed to trigger bulb formation. Short-day onions grow best in the southern United States, between 25° and 35° north latitude, and start bulbs when day length reaches 10 to 12 hours. The earlier that short-day onions are planted, the larger they get. In the South, onions can be planted in the fall and overwintered. Since they continue to grow throughout the winter, they will be ready for harvest in the spring.  

Intermediate, or day-neutral, onions are best suited to the middle tier of U.S. states, approximately between latitudes 32° and 42°, and start bulbs when day length reaches 12 to 14 hours. 

Long-day onions grow best in the northern states, between latitudes 37° and 47°, and start bulbs when day length reaches 14 to 16 hours. 

Do not try to fool Mother Nature: Short-day onions planted in a long-day zone will result in small bulbs—not an early harvest. 

Long-day varieties:

• ‘Yellow Sweet Spanish’: large, round shape; yellow-white.
• ‘First Edition’: high-yielding, stores well, flavorful, creamy-yellow
• ‘Red Wethersfield’: flat bulbs that store well, white flesh, red-skinned
• ‘Aisa Craig,’ ‘Walla Walla’: huge bulbs
• ‘Buffalo,’ ‘Norstar’: produce early but keep only until late December
• ‘Copra,’ ‘Southport Red Globe,’ ‘Sweet Sandwich,’ ‘Yellow Globe’: keep well
• ‘Red Florence’: heirloom; 4- to 6-inch long, dark purple-red, torpedo shape; mild, sweet
• ‘Ailsa Craig’: heirloom; named for a Scottish island; large, up to 8 inches in diameter; average 2 pounds; pale yellow skin, globe shape; mild, sweet 
• ‘Gold Coin’: cipollini; 1 1/2- to 3-inch yellow flattened bulb; pungent flavor sweetens when cooked

Short-day varieties:

• ‘Stuttgarter’: sold in sets, early maturity with a slightly flat shape, yellow
• ‘White Bermuda’: extremely mild, with thick, flat bulbs; white
• ‘Red Burgundy’: good table onion with mild, sweet white inside; short-term keeper
• ‘Crystal Wax White Bermuda’: a great onion for pickling when harvested at “pearl” size
• ‘Hybrid Yellow Granex’: sweet, Vidalia type
• ‘Red Creole’: heirloom; 3- to 4-inch, dark red globe shape; pungent
• ‘Southern Belle’: ruby color throughout
• ‘Texas 1015-Y Supersweet’: stores well
• ‘Yellow Granex’: Vidalia type; 3- to 4-inch, yellow, flattened globe shape; crisp; said to be the sweetest of the super sweet

Day-neutral or intermediate  varieties:

• ‘Candy’: golden, thick-flesh, jumbo bulbs; stores well
• ‘Red Stockton’: large, red-ringed, white-flesh bulbs
• ‘Super Star’: large, sweet, white bulbs
• ‘Purplette’: mini onion, at 1 1/2 inches; glossy, burgundy red when raw; pastel pink when cooked or pickled; mild, sweet
• ‘Southport Yellow Globe’: early; 2 1/2- to 3 1/2-inch thick-skin yellow globe; mild, sweet