Vegetable

Growing onions

Allium cepa · Amaryllidaceae
By Hannah Price · Updated 12 November 2026

Onions calendar

Onions sowing, planting and harvest calendar (UK)
	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Sow indoors	Sow indoors in January	Sow indoors in February
Sow outside			Sow outside in March	Sow outside in April
Plant			Plant in March	Plant in April					Plant in September	Plant in October
Harvest						Harvest in June	Harvest in July	Harvest in August

Timings suit lowland southern and central Britain and most of Ireland. In northern England and Scotland, or in a cold spot, start two to three weeks later in spring and finish earlier in autumn.

Overview

Onions can be grown from seed, which is cheap and offers more choice, or from sets, which are small bulbs grown the previous year and much easier for beginners. Spring-planted onions are the main storing crop, while autumn sets sit through winter and fill the gap in early summer when stored onions are running out.

Varieties to try

'Sturon' and 'Centurion' are reliable brown onions from spring sets that store well. 'Red Baron' gives deep red bulbs with a mild flavour. For autumn planting, 'Radar' is very hardy and 'Electric' is a red alternative. If you sow from seed, 'Ailsa Craig' can grow into large, mild bulbs, while 'Bedfordshire Champion' is a long-standing storer.

Soil and site

Best soil: Firm, well-drained, fertile soil that was manured for a previous crop.

Choose a sunny bed with good drainage. Onions dislike freshly manured or loose soil, so use ground that was improved for a previous crop and tread it firm before planting. Rotate them with other alliums such as garlic and leeks, and avoid any spot where white rot has appeared before.

Sowing and planting

Plant spring sets in March or April, pushing each one into the soil so only the tip shows. Plant autumn sets in September or October. Seed can be sown in modules indoors in January or February, four or five seeds per cell, then planted out as a clump in April. Outdoors, sow thinly in drills in March or April and thin seedlings in stages.

Spacing: Sets 10 cm apart with the tips just visible; closer spacing gives smaller bulbs that store well.

Care

Birds sometimes pull up newly planted sets, so cover rows with fleece or netting for the first couple of weeks and replant any that are lifted. Hoe or hand weed often, because onions have sparse leaves and cannot compete. Water only in long dry spells, and stop altogether once bulbs swell in July. Snap off any flower stems that appear.

Harvesting and storing

When the leaves yellow and flop over, ease the bulbs from the soil with a fork and lay them in the sun to dry for a couple of weeks, bringing them under cover if rain is forecast. Once the skins rustle and the necks are dry, store them in nets, trays or plaits somewhere cool and airy. Use any thick-necked bulbs first.

Common problems

Onion rust shows as orange flecks on leaves in late summer; clear debris and avoid overcrowding. Onion white rot is a soil-borne fungus with no cure, so never move soil or plants from an infected bed. Downy mildew and onion fly can also cause trouble in some years.

Read more on the problems that most often hit onions:

Not sure what you're looking at? Try diagnosing it by symptom.

Month-by-month reminders

Jobs for onions come round in January, February, March, April, June, July, August, September and October. Each month page lists the rest of the garden's jobs for the same weeks.

Grow alongside

Sources

Names follow Kew's Plants of the World Online; timings and spacings reflect UK growing practice and were checked against the references below. Text is our own. See our editorial policy.