Onion

Growing facts

Scientific name

Allium cepa

Origin

Central Asia

Plant size

12–24 in upright hollow leaves over a bulb

Growth rate

Slow to medium

Sun

Full sun

Soil

Loose, rich, well-drained soil; keep weeds down, as onions compete poorly

Soil pH

6.0–7.0

Pollination

Not needed for bulbs

Cold hardiness

Frost-hardy; young plants take temperatures into the 20s °F

USDA zones

Cool-season crop in all zones; pick short-day types for zones 8–11 and long-day types for zones 6 and colder

Harvest

90–120 days from transplant for bulbs; green onions in 30–60 days

When to plant (zones 9–11)

Sep–Jan

When to plant (zones 5–8)

Mar–Apr

Water

About every 3 days once established, without rain; more in heat, in pots and while young

Feeding

About every 21 days

Taste

Sweet types are mild enough to eat raw; storage types are pungent and sweeten when cooked

Nutrition

Vitamin C, fiber and flavonoids like quercetin (more in red onions)

Is onion safe to eat? Edible and toxic parts

What you can eat

• Bulbs, raw or cooked
• Green tops, like scallions
• Flower buds and flowers

Toxic parts and cautions

• Toxic: Toxic to dogs and cats. Onions, garlic, chives and leeks damage red blood cells and can cause anemia days after eating, raw, cooked or powdered. Cats and Japanese dog breeds are most sensitive. Call a vet if a pet eats a meaningful amount.
• Good to know: Onions can trigger heartburn and IBS symptoms for some people.

Pets: Toxic to dogs and cats in every form: raw, cooked, dried or powdered. Watch for weakness, pale gums or red urine a few days after eating.

How to eat and enjoy onion

• The base of countless dishes: sofrito, mirepoix, curry
• Caramelized onions and French onion soup
• Raw in salads and salsas (sweet types)
• Onion rings
• Pickled red onions

Onion varieties (6)

• Candy

  A large, sweet yellow onion that bulbs across a wide range of latitudes.

  Taste: Sweet

  Intermediate-day; grows in much of the middle of the country.

• Red Creole

  A short-day red onion with pungent flavor.

  Taste: Pungent

  Short-day; stores better than most Southern onions.

• Texas Early Grano · also Texas Grano 502, Texas Early White

  A short-day, mild onion with large, top-shaped bulbs.

  Short-day; a good Florida and Gulf Coast choice. Doesn't store long.

• Texas Super Sweet · also 1015Y, Texas 1015

  A big, round, very sweet short-day onion.

  Taste: Sweet, mild

  Short-day; resists pink root.

• Walla Walla · also Walla Walla Sweet

  A big, flattened, very sweet onion.

  Origin: Washington · Taste: Very sweet, juicy

  Long-day; for northern gardens. Doesn't store long.

• Yellow Granex · also Granex, Vidalia

  The flattened, sweet short-day onion grown as the Vidalia onion in Georgia.

  Taste: Very sweet, mild

  Short-day. Eat within a few weeks.

Pests and diseases to watch for

• Scale insects

  Small bumps, waxy or shell-like, on stems and leaf veins; sticky honeydew and black sooty mold below.

  What to do: Scrub small colonies off with a soft brush.

• Mealybugs

  White cottony clusters in leaf joints, under leaves and on fruit stems; honeydew and sooty mold.

  What to do: Blast off with a strong spray of water.

• Aphids

  Clusters of tiny soft insects on new shoots; leaves curl and get sticky.

  What to do: Spray off with water.

• Sooty mold

  Black, papery film on leaves and fruit that wipes off; it grows on honeydew.

  What to do: Control the insects making honeydew; the mold then weathers away.

• Spider mites

  Fine pale speckling on leaves, dusty undersides and fine webbing; leaves bronze and drop.

  What to do: Hose the undersides of leaves.