Onion — Vegetables

Allium cepa

Full sun, light watering — hardy in most of the UK.

Photograph of Onion — iNaturalist / GBIF

Plant out: Mar
Harvest: Aug

Sun: Full sun
Water: Low
Difficulty: Demanding
Hardiness: H4
Season: spring
Height: 10–50 cm
Spacing: 50 cm
Pets: Toxic to pets

Grows well with

Broccoli — Onions grown with broccoli cut the damage done by cabbage looper and cabbageworm caterpillars in a field study.Carrot — The scent of onions is often said to stop carrot fly finding your carrots. Trials have not found this reliably, so do not count on it - a fine mesh cover is what actually keeps the fly off.Courgette — Onions are named as a suitable partner for courgettes, so a row of them along the edge of the courgette bed works well.French Bean — Onions and dwarf French beans are a long-standing bad pairing - give them separate zones rather than the same row.Brassicas — Keep your onions out of the cabbage zone: onions next to brassicas is listed among the combinations that do not work.Potato — Onions grown in among potatoes brought aphid numbers down in a trial. Scent drifting from the undamaged onions changes the smell of the potato foliage, and aphids avoid it.

Growing notes

Grows to 0.1-0.5 metres. Space about 10-50cm apart. At its best in spring.

Toxic to pets

Onions damage the red blood cells of a dog or cat, raw or cooked, so keep onions and any scraps or peelings out of reach. The record lists no hazard to people. If a pet eats any, contact a vet straight away.

→ Your vet or the Animal PoisonLine