The onion is an easy-to-grow vegetable that’s big on flavor. Whether you grow sweet onions or storage onions, fresh onions are delicious on salads, sautéed, or caramelized in a variety of savory dishes. Plant a diverse crop of onions, including a variety or two that stores well, and enjoy garden-fresh onions year-round. Full sun and moist, well-drained soil are all you need for a prolific onion crop.
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Onions are generally classified as short-day and long-day varieties. Onions begin to form bulbs based on the amount of daylight they receive. Short-day varieties require 10 to 12 hours of daylight to produce bulbs, while long-day varieties need 14 hours or more. Generally long-day types are grown in cool climates because they produce large bulbs over a long period of time while short-day types are great for warm climates where they will quickly produce a robust crop. There are many different storage and fresh-eating varieties of onions within each category.
Onions thrive in full sun and moist, well-drained soil. Loose soil that freely drains is essential; onion bulbs will rot in clay and slow-draining soil. Plant onions in raised beds or containers if garden soil drains poorly. Onions can grow well in a container; choose a pot that is at least 16 inches in diameter and 12 inches deep.
Onions can be grown from seed planted indoors or outdoors, or they can be started from sets or bulbs for a jump start on the growing season. In cold climates, onions must be started indoors 10 to 12 weeks before the average last frost date or started from sets or bulbs to ensure a mature crop before the fall frost. To sow seeds indoors or out, plant them ¾ inch deep in loose, moist soil. In the garden after seedlings emerge, thin them to 3–4 inches apart in the garden. Transplant seeds started indoors into the garden a couple of weeks before the average last frost date—onions tolerate light frost.
Plant bulbs or sets in the garden two to three weeks before the average last frost date. Water plants well and spread a 2-inch-thick layer of mulch around newly planted bulbs or sets to prevent weeds. Water plants regularly throughout the growing season, providing a deep watering weekly if it does not rain.
Harvest onions whole when about half the tops are dry and are falling over. Undercut and lift the bulbs with a spading fork if they are not easy to pull. Cure storage onions by leaving them in a warm, well-ventilated area for two to four weeks until the outer bulb scales are dry. Store onions in a cool, dry area.
More Varieties of Onion
Allium cepa 'Ambition' produces divided bulbs with reddish-copper skin and white flesh. 90 days
'Candy Hybrid' onion
This variety is a mild-flavor intermediate-day yellow onion. It stores fairly well. 85 days
'Copra Hybrid' onion
Allium cepa 'Copra Hybrid' is a widely adapted long-day yellow storage onion that is sweeter than most other storage onions. 105 days
Egyptian walking onion
This cultivar develops a cluster of onion bulblets at the tips of 2-foot-long stems. The weight of the bulblets causes the stem to bend, allowing the small onions to root in the ground and gradually spread from the mother plant, hence the walking onion name. The bulblets can be used as you would pearl onions. Or harvest the green stems when they are tender to use as green onions.
'Evergreen Hardy White' scallion
Allium cepa 'Evergreen Hardy White' is a perennial you plant in spring or fall. It's ready to harvest about 65 days after a spring planting.
'Giant Red Hamburger' onion
This cultivar bears dark red bulbs that are good for slicing. The interior flesh is white and sweet. It is best adapted to the South. 95 days
'Redwing Hybrid' onion
Allium cepa 'Redwing Hybrid' has pungent, red-flesh bulbs that store well. 110 days
'Superstar Hybrid' onion
This variety produces huge white bulbs that weigh up to 1 pound each. It is day-neutral, so it can be planted anywhere. 100 days