How to grow onions from seed

Overview

Onions are easy and cheap to grow, whether from seed or from heat-treated sets. Follow our step-by-step guide, below, on growing onions from seed (skip to Step 3 for instructions on planting out sets).

Onion sets are miniature or immature onions, which can be planted out in March or April for a quick-growing crop. Sets are available from garden centres or by mail order, and although the range of varieties is not quite as wide as from seed, it's is an easy, reliable method of growing.

Whether you grow from seeds or sets, you can start to harvest bulbs in early summer and have plenty to store through winter.

As with the majority of vegetables, onions grow best in a well-lit position, with soil that has been enriched with generous amounts of plenty of organic matter.


How to do it

Sowing onion seeds into a modular seed tray

1Sow seed in a pot or tray of seed compost. The seeds are small, but try and space them about 1cm apart. Lightly cover with a thin layer of compost then stand pot or tray in water to moisten.


Transplanting onions seedlings into prepared soil outdoors

2When the seedlings are a few inches tall, prick them out and transplant into fresh compost. Once established, transplant seedlings into the garden, 10-15cm apart.


Planting onion sets

3Alternatively, in spring, plant heat-treated onion sets, into soil that has had large stones and weeds removed, and been enriched with organic matter. Plant each set 10-15cm apart, with tip protruding. Water newly planted sets and cover immediately with horticultural fleece, to prevent birds from lifting them. Once firmly rooted, the developing crops can be uncovered.


Watering onions seedlings

4Using a watering can with a rose, thoroughly water seedlings and sets directly after planting to settle soil around roots or bulbs. Repeat at regular intervals if the weather is dry.


Hoeing around developing onions with a circle hoe

5Hoe regularly to remove weeds, which will compete for water and nutrients with developing bulbs. A hand-held 'onion hoe' or 'circle hoe' are both perfect for weeding in small spaces.


Harvesting mature leeks

6In late summer, draw away earth from the bulbs to expose them to the sun. Harvest after the leaves turn yellow and the stem bends over. Allow leaves to dry before carefully lifting bulbs.


Adam's tip

Onions need a sunny, well-drained spot. They will crop on clay soil, provided it doesn't get too wet. They can run to seed or 'bolt' on light soils
Remove any attached soil and allow the onions to dry off thoroughly before storing
Once dried, a convenient way to store onions is to string them up in onions ropes and hang them in a cool, dry, frost-free place. Select only unblemished bulbs with narrow, well-closed necks. Wide-necked onions do not store well so use them first



Discuss this project

Talkback: How to grow onions from seed
Your comment will appear after a quick registration step

carfras 29/05/2012 at 10:24

do you expose all of the onions in late summer ?or just the soil around the tops..and how long do you leave the onions there before you dig them up...

joannep 13/04/2014 at 19:34

How deep do you repot your onion seedlings