Onion

Allium cepa · Vegetable

A kitchen staple grown from seed, sets or transplants. Bulb size depends on day length, so pick short-, intermediate- or long-day varieties to match your latitude. Weeds are its main competitor.

💧WaterWeekly, about 1 in (estimated)

☀️LightFull sun, 6–8+ hours

🐾PetsToxic

Care at a glance

Light: Full sun, 6–8+ hours
Water: About 1 in per week; stop when tops fall
Soil: Loose, weed-free, pH 6.0–7.0
Temperature: Best 55–75 °F; young plants tolerate light frost
Spacing: 4–6 in apart, rows 12–18 in
Container: At least 2 gallons, 8 in deep
Harvest: 90–120 days from sets or transplants (estimated)
Lifespan: Biennial grown as annual

When?

Plant sets or transplants in early spring, 2–4 weeks before the last frost. In mild-winter areas, short-day types are planted in autumn for an early summer crop (estimated).

Step by step

Prepare loose soil and remove all weeds.
Push sets in so the tip just shows, 4–6 in apart.
Keep the bed weed-free; onions have shallow roots and compete poorly.
Water steadily during bulb formation.
Avoid heavy nitrogen once bulbs start to swell.
Remove any flower stalks as soon as they appear.
When most tops fall over, lift bulbs and cure them in a dry, airy spot for 2–3 weeks.

Common problems

Plants flower earlyCold spells or large sets; use smaller sets, remove stalks.

Silvery streaks on leavesThrips; spray with water and keep plants unstressed.

Bulbs rot in storageNot fully cured; dry until necks are tight and papery.

Tunnels in bulbsOnion fly larvae; rotate beds and use fine netting.

Pets

Toxic to cats and dogs in all forms, raw or cooked; can damage red blood cells. Keep away from pets. If in doubt, ask your vet.

Similar plants

Garlic Chives Carrot

Sources

ASPCA — Toxic and Non-Toxic Plants

This page is general guidance; no pesticide doses are given.