When to Plant Onion in Canberra — Cold / Highland Guide

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.

Current Growing Conditions

Soil temperature: 18.9°C (optimal range: 8–30°C) ✓ Ready to plant

How to Grow Onion in Cold / Highland Australia

When to Plant

Sow seed under cover June-August. Transplant September-October after last frost. Or sow autumn (March-April) for overwintering types if frost protection available.

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

Cold / Highland Growing Tips for Onion

Recommended Varieties

  • Pukekohe Long Keeper (long-day)
  • Ailsa Craig (long-day)
  • Creamgold (intermediate)
  • Red Baron
  • Sturon

Key Challenges

  • Short growing season due to frost
  • Cold, wet soil delaying germination
  • Need for vernalisation (cold period) for seed saving but risk of bolting in crop year

Pro Tips

  • Start seeds indoors or in a greenhouse 8-10 weeks before transplanting
  • Use cloches or row cover for early spring protection
  • Long-day varieties thrive with the long summer days at highland latitudes

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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