When to Plant Onion in Cairns — Tropical Guide
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.
Current Growing Conditions
Soil temperature: 25.2°C (optimal range: 8–30°C) ✓ Ready to plant
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.
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