For generations, keen show-growers have sown their first onions on Boxing Day with dreams of prize-winning bulbs in summer. Sowing this early gives the exhibition varieties plenty of time to bulk up to truly spectacular sizes. But even if you’re only planning to grow onions for your own kitchen, sowing onions on Boxing Day is an excellent excuse to get out of the house and work off some of your Christmas dinners!
Why grow onions from seed?
Growing onions from seed involve a little more work than planting sets in spring, but it has some advantages:
- If you’re planning to grow a big crop of onions, a packet of seed is much more cost-effective than buying sets.
- There’s a wide variety of onion seeds to choose from, including interesting heritage varieties.
- Onions grown from seed are less prone to bolt (i.e. to flower and set seed instead of developing a bulb) than onions grown from sets.
How to grow onions from seed
If you’re sowing onions on Boxing Day (or any time in mid-winter), you’ll need to start them off somewhere warm, like a heated greenhouse or a propagator.
- Fill seed trays with good multipurpose compost. Sow the seeds, 5-6 per module and cover them lightly with a thin layer of compost. Water and place somewhere at a temp of 10-16 C (50-61F).
- In spring, harden off the seedlings and plant them out in well-drained soil in full sun. Although onions are hardy, they will benefit from being covered with fleece while young to protect them from hard frosts. In dry spells, water fortnightly and feed occasionally with a balanced liquid fertiliser.
- Once the onions thrive, thin the clumps so that you are left with one or two onions in each clump, the onions that you pull up can be used as spring onions. Weed regularly, preferably by hand, to avoid damaging the roots of your onions. Remove any flower stems as they appear to ensure all the plants’ energies go into producing bulbs.
- Once the bulbs start to swell in midsummer, stop feeding and watering. When the leaves begin to yellow and flop over, they are ready to harvest.
- First, to store onions, leave them out in the sun or in a greenhouse for two weeks to ripen. Store the bulbs in net bags once the foliage is dry and papery, or tie the leaves together and hang up somewhere light, dry and cool. Don’t store bruised or damaged onions.
Onions to sow in winter
These reliable varieties are perennially popular with both show-growers and cooks.
- Onion ‘Ailsa Craig’ – large bulbs with golden-brown skins and a mild flavour, popular with show growers and cooks
- Onion ‘Exhibition’ – a traditional show-growing variety producing large, golden-skinned bulbs
- Onion ‘Red Baron’ AGM – a late-maturing variety with flavourful dark red bulbs.