Grow onions for garden-fresh cooking

By Diana Stoll
Updated 4/20/2018 6:14 AM
  • Onions push up through the soil as bulbs enlarge.

    Onions push up through the soil as bulbs enlarge. Courtesy of Diana Stoll

Growing onions is easy. A cool-season crop, they can be planted by direct seeding, sets or transplants early in spring.

Plant them in a sunny spot with well-drained soil. Amend with organic matter and mix in fertilizer high in nitrogen when planting. Planting in mounded rows, raised beds and containers are good options for gardens with undesirable soil.

Growing onions from seed gives gardeners the largest choice of cultivars but requires up to four months to harvest. Start onion seeds indoors six to eight weeks before planting outside. Plant seeds about one-quarter inch deep, keeping the soil moist and trimming back foliage as it grows to keep it about 4 inches tall. Thin seedlings so plants grow 4 to 5 inches apart.

Transplants are sold in bunches. If they won't be planted right after they are purchased, put them in a large pot with a couple inches of moist soil in the bottom. Store them in a cool spot with bright light but not direct sunlight.

The largest transplants produce the biggest bulbs. Plant them an inch deep with their "necks" barely covered. Space plants at least six inches apart in 1-foot-wide rows so they will have room to grow top size onions. To harvest seedlings as green onions, space them just a couple inches apart.

I think planting sets (immature bulbs grown the year before) is the easiest way to plant onions. They are also the earliest to mature. Sets are usually purchased by color -- red, yellow or white -- instead of by specific cultivar name. When purchasing onion sets, chose ones that are firm, the size of marbles and not already sprouting.

Sets can be planted before the last frost date if the soil is warm enough and ready to be worked. Space them about 4 inches apart in 1-foot-wide rows.

Regardless of the form in which they are planted, onions are heavy feeders. Fertilize them with a high-nitrogen fertilizer every few weeks. Stop feeding when they start producing bulbs.

Onions are shallow rooted so keep the soil slightly moist until their bulbs have enlarged. A layer of mulch will help the soil retain moisture longer. The amount of water available to onions also affects their flavor. More water results in sweeter onions; drought-stressed onions taste stronger.

Onions can be harvested at any time. I plant onions a little too close together and then harvest every other plant as green onions, opening space for the others to grow. Once mature, the foliage yellows and falls over. When more than half of the leaves have fallen, it is about time to harvest.

Manually bend the rest of the stems over to hasten the ripening process of those plants. Leaving foliage attached, dig onions, remove loose soil and put them in a warm, dry place with good air circulation. Of course, feel free to eat a few right away.

Onions are ready for storage once their outer skins have dried. Wipe off any remaining soil and remove the tops before storing them in a cool, dry spot -- temperatures of 40 to 50 degrees are best. Don't store onions with apples or other fruits or vegetables. Apples give off ethylene gas as they ripen, and onions may affect the flavor of other produce in storage.

If given proper cultural conditions, onions have few problems and are rarely assaulted by insects or disease. Onions rot in damp soil and may split in periods of drought. Sometimes thrips feed on leaves, causing them to curl. Neem oil, spinosad and insecticidal soap may help control them. Apply according to labeled directions.

We slice and dice onions to use fresh and cook in a wide variety of dishes -- everything from omelets and French onion soup to topping our pizzas and hamburgers. We eat them all by themselves as onion rings and blooming onions. My dad used to eat onion sandwiches!

Plant enough for all the ways your family eats onions.

• Diana Stoll is a horticulturist, garden writer and speaker. She blogs at

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