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Onion growing in a garden
Annual vegetable

Onion plant profile

Allium cepa

An annual vegetable for full sun.

Last updated .

When to plant

When to plant Onion

Onions are a cool-season crop planted early. Sow seed outdoors in early spring, or set out sets and transplants in April; transplants need roughly 8 weeks of growth beforehand (USU, UMN).

The calendar shows this cited seasonal window as an approximate band. It does not convert the season into frost-adjusted dates.

Open Onion in my garden calendar

Shows the source-backed planting season, not frost-adjusted dates.

Growing conditions

Sun
Full sun
Water
1 in / week
Planting depth
0.25 in
Soil pH
6 to 7
Lifecycle
Annual
Spacing
3 to 4 in apart, rows 8 in
Days to maturity
100 to 120 days (from sowing)

Common problems

Watch for these

Also watch for: neck rot, basal rot, pink root.

Evidence trail

Evidence behind this profile

Original extension and institutional publications behind the planting, care, and safety facts on this page.

  1. How to Grow Onions in Your Garden

    Utah State University Extension. Supports general reference. Checked 2026-06-11.

  2. Growing onions in home gardens

    University of Minnesota Extension. Supports general reference. Checked 2026-06-11.

  3. Toxic and Non-Toxic Plants: Onion (Allium cepa) entry

    ASPCA Animal Poison Control Center. Supports pet-safety verdicts for dogs and cats. Checked 2026-07-18.