When to plant Onion in Cool Australia

Cool zone — applies to Hobart, Canberra, Ballarat, Orange, Armidale and similar areas. Growing elsewhere? Temperate · Subtropical · Tropical · Arid.

Sow onion seed direct from February to October in the cool zone — an unusually generous window, though 160–230 days to maturity means this is a slow, patient crop whichever end you choose. Seed germinates in 10–20 days sown just 5 mm deep, and seedlings are thinned to 5–10 cm. Autumn sowings in Canberra or Hobart overwinter as pencil-thin seedlings and bulb up the following spring; late-winter and spring sowings mature into autumn. Match variety to timing — early, mid-season and late types respond to different day lengths, so check the packet.

Sowing calendar — cool zone

Green months are your sowing window: February to October.

Growing notes

Onions are hardy and completely untroubled by cool-zone frost — seedlings sit through a Canberra winter without protection — but the calendar still needs thought because of the crop's sheer duration: 160–230 days from seed. Autumn sowings between February and April overwinter small and bulb the following spring; sowings from late winter through October mature across the following summer and autumn. Either way the bed is occupied for the better part of a year, so site onions where they won't be in the way.

The characteristic cool-climate failure is bolting. If autumn-sown seedlings grow too large before winter — thicker than a pencil — the cold vernalises them, and in spring they throw a flower stalk instead of a bulb. The fix is timing: sow late enough in autumn that plants enter winter small, or shift to a spring sowing. Bolted onions won't store, though they're fine used fresh.

Sow shallow at 5 mm into firm, weed-free soil in full sun, and thin to 5–10 cm. Onions root shallowly and compete badly, so weed little and often by hand rather than with a hoe. Ease off watering as the tops begin to fall over, then lift and cure bulbs in an airy, dry spot for a couple of weeks — properly cured cool-climate onions keep for months.

Onion at a glance

Companion planting

Grows well with

Carrot: Scent of each deters the other's primary pest (carrot fly, onion fly)

Chamomile: Improves onion growth and flavour

Beet: Efficient space use; onions deter leaf miners that attack beet

Keep away from

Bean (Bush): Alliums inhibit nitrogen-fixing bacteria essential to beans

Bean (Climbing): Alliums inhibit nitrogen-fixing bacteria

Peas: Alliums inhibit legume growth

Common questions

When should I sow onions in Canberra?

Any time from February to October. Autumn sowings overwinter as small seedlings and bulb in spring, while late-winter and spring sowings mature the following autumn. Onions take 160–230 days, so plan for a long occupation of the bed.

Why did my onions go to seed instead of forming bulbs?

They bolted — seedlings that grow thicker than a pencil before winter get vernalised by the cold and flower in spring. Sow a little later in autumn so plants stay small over winter, or sow in spring instead.

How long do onions take to grow from seed?

Between 160 and 230 days depending on variety and season. Germination alone takes 10–20 days, so patience is part of the deal; the payoff is that cured bulbs store for months.

Can onion seedlings survive frost?

Yes, onions are hardy and cool-zone frosts don't bother them at any stage. Seedlings overwinter in the open without protection, even in heavy-frost districts.

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