When to plant Onion in Arid Australia

Arid zone — applies to Alice Springs, Mildura, Broken Hill, Kalgoorlie, Port Augusta and similar areas. Growing elsewhere? Temperate · Cool · Subtropical · Tropical.

Direct-sow onion seed from February to August in the arid zone, just 5 mm deep — late summer through winter, so the long growing season runs through the cool months rather than the furnace. And it is long: onions need 160–230 days from seed, the slowest crop in most dry-country gardens. Germination takes 10–20 days. Fully hardy, they lose nothing to the frosty winter nights of Broken Hill or Port Augusta; seedlings simply sit and thicken through the cold. Space plants 5–10 cm apart in rows 25–40 cm apart, and be patient — bulbing waits on spring day length, not on you.

Sowing calendar — arid zone

Green months are your sowing window: February to August.

Growing notes

Onions suit arid gardens better than their timeline suggests. Hardy seedlings coast through freezing desert nights unharmed, dry air keeps downy mildew away, and the crop's whole schedule — establish in autumn, sit through winter, bulb in spring, cure in early summer heat — maps neatly onto the dry-country year. Around Port Augusta the harvest lands in genuinely rain-free curing weather, which is why cured onions from arid gardens store so well.

Two things go wrong. First, weeds: an onion seedling is a single grass-like thread for months, and in an irrigated bed surrounded by desert, weeds treat your drip line as an oasis. A crop lost to weed competition is the most common failure, so hand-weed fortnightly early on — onion roots are shallow and hate hoes. Second, moisture checks: those shallow roots occupy the top 15 cm of soil, which in low humidity dries daily even in winter. Water little and often rather than deep and rarely (the opposite of the tomato rule), and hold 30–50 mm of fine mulch around the plants without burying the developing bulb shoulders.

Within the window, February–April sowings make the biggest bulbs. Sowing after August is pointless — lengthening days trigger bulbing before the plant has any size, and you harvest marbles. Stop watering when the tops fall over, then let the summer sun do the curing.

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 the arid zone?

February to August, with late summer and autumn sowings producing the largest bulbs. Sown later than August, plants bulb up while still tiny and you get very small onions.

How long do onions take to grow from seed?

160–230 days — the better part of eight months for some varieties. Germination alone takes 10–20 days, so mark the row and don't give up on it.

Will frost damage my onion seedlings in Broken Hill?

No. Onions are fully hardy and handle inland winter frosts without protection. They grow slowly through the cold and accelerate into bulbing as spring days lengthen.

Why did my onions stay tiny?

Usually weed competition while seedlings were small, or sowing too late in winter. Keep the bed hand-weeded early, and sow by autumn so plants have real size before spring day length triggers bulbing.

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