Why some gardeners sow onions on Boxing Day

There’s a long-standing tradition among show growers to sow onions on Boxing Day.

The thinking is straightforward: onions are slow-growing, and starting them early gives them the longest possible season to bulk up. If you’re aiming for large, well-developed bulbs, that head start can make a noticeable difference.

Boxing Day also happens to be a good moment for it. The busyness of Christmas has passed, the pace drops, and there’s often a quiet window where a small, intentional job feels welcome rather than demanding. A tray of onions fits neatly into that gap.

I’m not actually sowing onions on Boxing Day myself this year.

I sowed onions for overwintering back in August as a trial, and I’m interested to see how they perform next year. That earlier start scratches the same itch for me: giving the plants more time and seeing what effect it has. That said, I do still have some onion seed left over (Augusta) so whether I end up joining in anyway remains to be seen. It may yet turn into another experiment.

How to sow onions (if you’re doing Boxing Day onions)

If you do decide to sow now, keep it simple:

• Use a standard multipurpose compost in modules or a shallow tray.
• Sow thinly, either one or two seeds per module, or spaced out in rows if using a tray.
• Cover lightly with compost or vermiculite and water gently.
• A bit of warmth helps germination — around 10–16°C is ideal.
• Once germinated, move them somewhere cool and frost-free with as much light as possible.
• Thin seedlings if needed, leaving the strongest plants to grow on.
• Label them. Onion seedlings all look the same once they’re up.

Through winter they’ll put on slow, steady growth. In spring, harden them off gradually before planting out, giving them time to adjust to outdoor conditions.

And if you’re looking for a calm, low-pressure way to quietly mark the start of the growing year, Boxing Day onions fit that bill nicely. One tray, a few minutes, and the sense that something is already underway, all while the garden itself is still resting.