When to Plant Onion in Cairns, Tropical Guide

Sow April and June to July. Right now in September it is out of season. The next sowing month is April.

Also called spring onion, scallion, shallot (the Australian name for spring onion).

Published · Last reviewed · By Garden Buddy
Growing advice is reviewed by hand. Planting dates, current conditions and prices on this page update daily.

This Onion guide is written for the Tropical zone, which takes in Cairns, Townsville and Darwin. Somewhere else? Your postcode picks the right one.

Not your zone? Brisbane Sydney Melbourne Canberra Alice Springs Perth

Also handy: will it frost this week? and what grows in shade.

Onion

Photo: Wikimedia Commons

Onions are a staple in Australian kitchens and one of the most widely grown alliums in home gardens. Bulb formation is triggered by day length, making variety selection critical based on latitude. Short-day types suit northern Australia, while long-day types perform best in southern regions.

Planting Calendar for Tropical

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
- - - S - T T - - - - -

S = Seed Tray   T = Transplant   D = Direct Sow

Want a nudge when it is Onion sowing time in Cairns?

One email a week with what is worth planting in the Tropical zone right now, Onion included, plus which veg has jumped in price at the supermarket. Free, and you can stop it in one click.

Current Growing Conditions

Soil temperature: 21.4°C (optimal range: 8–30°C) ✓ Ready to plant

Modelled from Open-Meteo forecast (Cairns), not a live sensor.

How to Grow Onion in Tropical Australia

When to Plant

Plant short-day varieties February-May for the dry season. Bulb onions are genuinely difficult in the tropics due to minimal day length variation. Spring onions and shallots are far more reliable.

Soil
Well-drained, fertile loam enriched with compost. Avoid heavy clay or freshly manured soil which causes forking and soft bulbs.
pH Range
6.0-7.0
Sunlight
Full sun (minimum 6 hours direct)
Spacing
12cm apart, 30cm between rows
Watering
Consistent moisture during bulb development. Water deeply once or twice weekly. Reduce watering as tops begin to fall over (curing signal). Overhead irrigation can reduce thrips but increases fungal r

Companion plants: Carrot, Beetroot, Lettuce, Chamomile, Strawberry

Avoid planting near: Beans, Peas, Asparagus, Sage

Tropical Growing Tips for Onion

Recommended Varieties

  • Red Tropicana (short-day)
  • Texas Grano (short-day)
  • Gladalan Brown (short-day)
  • Spring onions/shallots (year-round)

Key Challenges

  • Insufficient day length variation for bulb formation in many varieties
  • High humidity drives fungal diseases
  • Thrips pressure year-round
  • Wet season waterlogging

Pro Tips

  • Focus on short-day varieties only. Long-day types will never bulb here
  • Spring onions and shallots are the most reliable allium crops
  • Raised beds are essential for drainage during wet season

Harvesting Onion

When ready: Tops fall over naturally and begin to yellow. Bulb skin is papery and dry. Neck tissue is thin and soft. Do not push tops over prematurely as this reduces storage life.

How to harvest: Loosen soil with a fork and lift gently. Do not pull by the tops. Lay on their side in the garden for 1-2 days if weather is dry, then move to a well-ventilated, shaded area for 2-4 weeks to cure fully. Roots and tops are trimmed after curing.

Worth growing?

A 2.4 m × 1.2 m bed fits 72 plants, about $29 worth at today’s Aldi, Coles and Woolworths prices, checked today.

That is roughly 11 kg at $2.66 a kilo.

Draw your onion bed → No account needed.

Where to next

What onion costs in the shops right now, retailer by retailer, updated daily.

Also worth sowing in the tropical zone this September: Lemongrass, Ginger, Cucumber and Basil.

The pest most likely to find your onion: Botrytis / Grey Mould.

Supermarket Price

Current average retail: $2.66/kg (12-month range: $1.99–$5.20)

Grow your own and save on grocery bills.

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Common Questions About Onion

When do you plant onion in Australia?

It depends on your climate zone, not the calendar month alone. Planting months by zone:

Does onion grow all year round in Cairns?

No. In the Tropical zone the planting months are Apr, Jun to Jul. Outside that window it either bolts, sulks or gets cut down by the weather.

What else is onion called?

Onion is the usual Australian name. Overseas seed packets and recipes call it spring onion, scallion, shallot (the Australian name for spring onion). Same plant, same growing advice.

Which zone am I in?

Type your postcode into the box under the heading and the page tells you, and links this crop in your own zone if it differs. Or look it up on the grow zone map. This page is the Tropical zone, Cairns is its reference city.