Onion

Allium cepa · Amaryllis family (Amaryllidaceae)

At a glance
Hardiness zones	2 to 11
Sun	full sun
Water	moderate
Life cycle	biennial
Frost	Hardy: takes frost
Soil pH	6.0–7.0
Spacing	3 to 4 inches
Days to harvest	90 to 120 days
Soil temperature to plant	at least 35°F

About Onion

Onions are grown from seed, transplants or small sets and are one of the first crops planted in spring. Bulbing is triggered by day length, so choose long-day types in the North and short-day types in the South.

Grown as a cool-season annual in every zone; match long-day varieties to the North and short-day varieties to the South.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Start seeds indoors: 12 to 14 weeks before the last frost
Set out plants: 2 to 4 weeks before the last frost
Sow seeds outdoors: 2 to 4 weeks before the last frost

Days count from planting for bulb onions; green onions are ready in about 50 days from seed. Seed started indoors needs 8 to 12 weeks before it goes out; sets and transplants go in as soon as the soil can be worked.

Soil

Well-drained, fertile soil high in organic matter, kept evenly moist.

Follow a soil test and keep pH about 6.0 to 7.0; work in up to 1 inch of compost, and without a test add about 1 lb of balanced fertilizer such as 10-10-10 per 100 sq ft into the top 6 inches.

Feeding

2 to 4 weeks after planting, once roots are well grown: nitrogen fertilizer such as 21-0-0. Spread about 3/4 lb (about 1 1/2 cups) per 100 ft of row about 6 inches from the plants, scratch it in and water.
1 to 2 weeks after the bulbs start to swell: fertilizer such as 5-10-10. Spread about 1 1/4 lb per 100 sq ft beside the row, about 6 inches from the plants, and water it in; stop feeding by midsummer.

Too much nitrogen, or feeding late in summer, gives late bulbs with thick necks that are soft and store poorly.

Harvest

Pull bulbs when about half the tops have fallen over and dried. Cure them in a warm (75 to 90F), airy spot for 2 to 4 weeks until the necks are tight and the outer skins papery.

Pull bulbs once, when about half the tops have fallen over and dried, then cure them 2 to 4 weeks in a warm, airy spot.

Varieties (41)

Variety	Type	Days	Notes
Beltsville Bunching	Bunching (non-bulbing)		Vigorous bunching onion bred for green onions. Listed with resistance to pink root, yellow dwarf, smut and thrips.
Evergreen White Bunching	Bunching (non-bulbing)	65 days	Does not form a bulb; makes clusters of slim white stalks. Very cold hardy and can overwinter.
Parade	Bunching (non-bulbing)	120 days	Bunching onion for green onions.
Cabernet	Intermediate-day		Intermediate-day onion recommended for Georgia.
Super Star	Intermediate-day (day-neutral), white sweet		Sweet. White sweet onion.
Candy	Intermediate-day (day-neutral), yellow sweet		Sweet. Yellow sweet onion.
Sierra Blanca	Intermediate-day, white	100 days	White onion listed as resistant to pink root.
Cimarron	Intermediate-day, yellow
Yula	Intermediate-day, yellow	103 days
Red Bull	Long-day, red
Southport Red Globe	Long-day, red		Red globe onion.
Redwing	Long-day, red storage		Red onion.
White Sweet Spanish	Long-day, white		Large white bulb.
Ailsa Craig	Long-day, yellow		Yellow onion; Wisconsin lists it as Ailsa Craig Exhibition.
Yellow Sweet Spanish	Long-day, yellow		Large yellow bulb.
Copra	Long-day, yellow storage		Yellow storage onion.
First Edition	Long-day, yellow storage		Flavor improves with cooking. High-yielding, with uniform globe bulbs and creamy-yellow flesh.
Patterson	Long-day, yellow storage
Walla Walla	Long-day, yellow sweet		Sweet and mild. Large yellow sweet onion from Washington State.
Burgermeister	Red	110 days	Large red onion.
Red Candy Apple	Red	95 days	Red onion recommended for Kentucky gardens.
Rossa di Milano	Red		Red onion that germinated well, matured early and yielded well in North Dakota trials.
Southern Belle	Red	110 days	Red bulbing onion grown from transplants in Central Texas.
Mars	Red storage (northern)		Red storage onion.
Red Burgundy	Short-day, red	110 days	Sweet. Large red bulb.
Red Creole	Short-day, red		Short-day red onion recommended for Georgia.
Contessa	Short-day, white		Open-pollinated short-day onion with large, white, deep-globe bulbs. Tolerates pink root and resists bolting.
Crystal Wax (White)	Short-day, white	60 days	Soft, mild white flesh. Flat, medium-size bulb with white skin and flesh.
Eclipse	Short-day, white	80 days	White short-day onion recommended in Texas.
Texas Early White	Short-day, white		White, top-shaped bulb.
White Bermuda	Short-day, white	95 days	Short-day white onion.
White Granex	Short-day, white sweet		Mild and sweet. Flattened bulb with pearly-white flesh; the white version of Yellow Granex.
Texas Early Grano 502	Short-day, yellow	80 days	Sweet. Large yellow bulb; the PRR strain resists pink root. Can also be pulled young as a green onion.
Granex 429	Short-day, yellow sweet	125 days	Mild and sweet. Hybrid with a flat, yellow-skinned bulb and white flesh. Tolerates some races of pink root.
NuMex Sweetpak	Short-day, yellow sweet		Low pungency (sweet). Firm, globe to flat-globe yellow bulb with light brown skin; good pink root resistance.
Texas 1015Y (Texas SuperSweet)	Short-day, yellow sweet	110 days	Sweet and mild. Large yellow globe. Resists pink root and keeps better than most short-day sweet onions.
Yellow Granex (Vidalia type)	Short-day, yellow sweet	100 days	Very mild and sweet; best eaten raw. Thick, flattened yellow bulb; the classic Vidalia-style onion. Granex 33 is a common hybrid strain and is prone to pink root.
Sweet Sandwich	Yellow	100 to 115 days	Yellow onion recommended in Kentucky, Utah and Wisconsin.
Talon	Yellow		Yellow onion that germinated quickly and was ready early in North Dakota trials.
Fiesta	Yellow, hybrid	100 days	Hybrid bulb onion recommended for Utah.
Ringmaster		120 days	Bulb onion on the Texas A&M list for Northeast and East Texas.

Good neighbors

Cabbage, Broccoli

UMN Extension cites studies where onions planted with cabbage or broccoli helped reduce caterpillar damage; evidence is modest.

Pests to watch for

Onion maggot, Thrips, Leafminers, Grasshoppers, Eriophyid mites (rust, bud, blister and gall mites), Mole crickets, Allium leafminer, Garden symphylan, Beet armyworm, Seedcorn maggot

Diseases and problems

Neck rot, Fusarium basal rot, Pink root, Bacterial soft rot, Bolting (going to seed), Aster yellows, Purple blotch, Cucumber mosaic

In the kitchen

A base flavor for countless dishes, eaten raw, sauteed, roasted, grilled or pickled.

Keeping it: Cure bulbs 2 to 3 weeks, then keep them in a cool (50-60F), dry, airy place in mesh bags or braids for months; check often for soft ones. Sweet onions keep poorly, so use them first, and don't store onions with potatoes.

Pets: Toxic to dogs, cats and horses (ASPCA): contains N-propyl disulfide, which damages red blood cells and can cause vomiting, anemia, weakness and a fast heart rate.

Sources

Photo: Photo: Stephen Ausmus, USDA ARS, Public domain (USDA ARS), via Wikimedia Commons. Photo resized for the web.

Planting dates and advice are general guidance; check with your local Cooperative Extension office for your area.