Packed with vibrant flavor, onions are a staple food throughout the world. Familiar bulb onions are easy to cultivate as long as you plant varieties adapted to your climate, and you can expand your onion season by growing leeks, scallions, and other non-bulbing varieties. Fertile, well-drained soil that’s slightly acidic (a pH between 6.0 and 6.8) is best for growing onions of all types.
Bulb Onion Types to Try
Bulb onions mature in response to changing amount of daylight. The longer the plants grow before they begin forming bulbs, the bigger and better those bulbs will be. In North America, days become shorter after the summer solstice, about June 21. Summer days are longer in the North than in the South.
Short-day varieties grow best in the South. They begin forming bulbs in late spring, so they need to be planted in fall in the far South and in late winter in colder climates in order to produce large bulbs.
Intermediate-day varieties are the best main-crop onions for the country’s midsection (Washington, D.C., to northern Arizona), and they can be grown as early onions in the North.
Long-day varieties are best grown in the North. These onions have spicy, well-rounded flavors and store well.
Check out our chart of alternative onions for information on growing leeks, scallions, shallots and other types of non-bulbing onions.
When to Plant Onions
In late winter, start seeds of all types of onions — bulb onions, leeks, scallions, and shallots — indoors under bright fluorescent lights. Make additional sowings until early spring. Set out bulb onion seedlings three weeks before your last frost, and set out seedlings of non-bulbing onions six weeks before your last frost.
In spring you can also plant sets, which are small, dormant onions. Small sets produce better bulbs than large sets do.
In fall, short-day varieties can be planted in many mild winter areas. Seedlings should be ready to set out in mid-October. For more details on when to plant onions in your region, visit our What to Plant Now page.