When to Plant Onion in Sydney — Warm Temperate 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: 19.3°C (optimal range: 8–30°C) ✓ Ready to plant
How to Grow Onion in Warm Temperate Australia
When to Plant
Sow March-May, transplant April-July. Intermediate-day varieties perform best. Some long-day varieties will work if planted early enough (March).
- 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
Warm Temperate Growing Tips for Onion
Recommended Varieties
- Creamgold (intermediate-day)
- Brown Spanish (intermediate)
- Early Lockyer White
- Red Burgundy
- Gladalan Brown
Key Challenges
- Getting timing right for day length response
- Downy mildew in humid autumn/winter
- Bolting in cold winters if plants are too large
Pro Tips
- Intermediate-day varieties are the sweet spot for Sydney region
- Sow seeds in March for transplanting in May-June
- Avoid transplanting seedlings thicker than a pencil to reduce bolting risk
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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