Growing Onions

Enlarge Image Image Gallery The robust, exceptional flavor onions add to meals is worth the few teardrops that may end up on your cutting board. Shown here, from left to right, are ‘Bianca di Maggio,’ ‘Red Torpedo,’ scallions, and a yellow onion with its stalk buds. KEITH WARD

Packed with vibrant flavor, onions are a staple food throughout the world. Familiar bulb onions are easy to grow as long as you plant varieties adapted to your climate, and you can expand your onion season by growing leeks, scallions and other types of non-bulbing onions. All onions grow best in fertile, well-drained soil that’s slightly acidic (a pH between 6.0 and 6.8).

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.

How to Plant Onions

Choose a sunny site with fertile, well-drained soil, and loosen the planting bed to at least 12 inches deep. Mix in a 1-inch layer of mature compost. Make a 4-inch-deep, V-shaped furrow in the prepared bed. Fill the bottom of the furrow with 1 inch of rich compost or a light dusting of dry organic fertilizer, and then water the prepared furrow. Set out seedlings or sets 3 to 6 inches apart, depending on the plants’ mature size.

Harvesting and Storing Onions

The tops of bulb onion plants fall over naturally once the bulbs have matured. When half of the tops in a planting have fallen over, lift all of the bulbs and place the pulled plants in a warm, dry place away from direct sunshine to cure.