How to Grow: Onions

One vegetable I use regularly in the kitchen is the onion (Allium cepa). That’s why growing them for me is so important. You can grow a wide variety of onions in our cool climate, from sweet red onions to pungent yellow onions. The flavor of fresh onions is incomparable. Give them well-drained soil, water, sun, and cool temperatures and they will reward you with an abundant crop for salads and cooking. They’re a

garden staple.

The key with growing onions is starting with the right variety. Onion varieties can be confusing because they are grouped as long, intermediate, or short day varieties. Short day varieties are planted in the fall in the South to mature in early summer. The famous ‘Vidalia’ onion is one of these. We usually don’t grow these around here. Long day varieties are planted in spring in the North to mature in mid summer. There are also intermediate or day neutral varieties that mature in summer from a spring planting regardless of where you grow them. You can also grow sweet or pungent varieties. Pungent varieties last longer in storage and are best for cooking. Sweet varieties should be eaten soon after harvest and are great raw in salads and in sandwiches.

If you love the taste of onions, but are intimidated by growing bulb onions, there are other easier allium choices. Scallions or green onions are grown for their mild flavored green tops. You can even grow varieties with purple stems. Shallots are small bulbs that produce more side bulbs around the main one over time. They’re simpler to grow and produce a mild flavor bulb, that’s less pungent than an onion.

When to Plant

Onions like growing in cool weather so start seeds indoors 6- to 8-weeks before your last frost date. You can also buy onion starts (small green plants) or sets (small bulbs). Whether you’re planting onion plants or sets, plant 3 weeks before your last frost date —late April or May.

Where to Plant

Onions grow and size up best in well-drained soil planted in full sun. They don’t like growing in wet soils, so build a raised bed 8 inches tall and 3-feet wide. Remove rocks, and debris from the beds before planting. Since onions are low growing plants, build your bed away from taller plants that may shade them later in the season.

How to Plant

The easiest way to grow bulb onions is by starting with sets. Sets are young bulbs the size of a quarter that you buy. You’ll have a limited number of varieties to grow, but they’re simple. Plant the sets, pointy side up, 2 inches deep in the soil. Space them 6-inches apart in rows 1 foot apart. Shallot bulbs have a similar look and feel as sets and are planted the same distance apart. Scallions (green onions) are planted from transplants or seed and are spaced 2 inches apart.

If you grow your own bulb onion seedlings or purchase ones at the garden center, plant then 2 inches apart in rows and thin, once they’re big enough to eat, so they’re ultimately spaced 6 inches apart.

Care and Maintenance

Onions don’t compete well with weeds, so it’s imperative to keep the bed hand weeded. They also need a constant supply of water, especially when the bulbs are getting larger, to make the biggest bulbs. Keep the beds well watered and mulch with a layer of straw to help prevent weeds from growing and keep the soil moist. Apply a high phosphorous plant food that also contains nitrogen, such as bone meal, to beds monthly to insure the onions grow large.

Onions only have a few pests that are cause for concern. Onion maggots are small worms that attack the bulbs tunneling holes in them. Spread sharp sand or diatomaceous Earth around the bulbs to kill them. Onions thrips are small aphid-like insects that feed on leaves. Spray insecticidal soap to kill these pests. Most disease problems are related to poor water drainage in the soil, so make sure the beds are loose and drain well. Also, rotate crops and grow disease resistant varieties to prevent disease problems.

Harvest

Scallions are easy to harvest. As soon as they grow 6- to 8-inches tall (about 2 months after planting), pull them out and enjoy in salads and stir fries. Shallots are harvested when the side bulbs that form around the planted bulb begin to separate and the leaves yellow. Pull the entire plant, separate out the side bulbs and store. You can grow specific varieties of scallions or just grow any onion and harvest the tops once they form. Of course, if you cut the tops of a bulbing onion repeatedly, you won’t get much of a bulb to form.

Bulbing onions should be harvested about 3 to 4 months after planting when one-half of the onion tops naturally fall over. Bend over the remaining tops and leave them for one week to cure in the garden. Then pull the onions out of the ground and dry them in a shady, airy, well ventilated room. Once dry, cut off the tops and store in a cool basement in mesh bags. Some varieties will last for up to 6 months in storage.

Additional Information

Some good scallion varieties to grow include ‘Evergreen Hardy’ with white stems and ‘Deep Purple’ with purple-tinged stems. ‘Ambition’ is a good shallot variety for our region.

For a great sweet onion you can’t beat ‘Walla Walla’. This yellow-skinned, white onion from Washington State features juicy sweet bulbs. ‘Alisa Craig Exhibition’ is a sweet variety hailing from Britain. ‘Candy’ is a day neutral variety that produces sweet, white fleshed bulbs. For a red sweet onion, try ‘Red Wing Hybrid’.

For storage onions with a naturally pungent flavor, ‘Copra Hybrid’ and ‘Cortland Hybrid’ are long time favorite yellow-skinned and white fleshed varieties. ‘Red Zepplin Hybrid’ is a new red skinned and fleshed storage onion that will last up to 6 months in storage. ‘Purplette’ is a small-sized onion that forms golf-ball sized bulbs within 2 months of planting.

If you’re looking for onion sets, you’ll find varieties such as ‘Sweet Sandwich’, ‘Yellow Spanish’, ‘Yellow Stuttgarter’ and ‘Red Wethersfield’ in garden centers and on-line. All are long day and good to grow in our climate.

Excepted from the Northeast Vegetable and Fruit Gardening book.