When to Plant Sunflower in Melbourne — Cool Temperate Guide

Sunflower

Photo: Wikimedia Commons

Sunflowers are dual-purpose annual plants grown for edible seeds and ornamental beauty. They are among the easiest and most rewarding plants for Australian gardens, growing rapidly from seed and producing spectacular flower heads that attract pollinators. Important note: sunflowers exhibit allelopathy - they release chemicals through roots and decomposing plant matter that inhibit the growth of certain nearby plants.

Current Growing Conditions

Soil temperature: 21.9°C (optimal range: 15–35°C) ✓ Ready to plant

How to Grow Sunflower in Cool Temperate Australia

When to Plant

Sow October-December after all frost risk passes. Soil must be warm (above 15C) for good germination.

Soil
Tolerates a wide range but prefers well-drained loam. Will grow in poor soil but produces larger heads in enriched soil. Remarkably drought-tolerant once established due to deep taproot.
pH Range
6.0-7.5
Sunlight
Full sun - minimum 6 hours, ideally 8+. Sunflowers are heliotropic (young heads follow the sun) and need maximum light for best growth.
Spacing
45cm apart, 75cm between rows
Watering
Water well at planting and during early growth. Once established (30cm+), sunflowers are surprisingly drought-tolerant. Deep weekly watering during head development and seed fill improves yield. Reduc

Companion plants: Corn, Squash/Pumpkin, Cucumber, Zinnia, Cosmos

Avoid planting near: Potato (allelopathic inhibition), Pole beans (allelopathic inhibition), Most brassicas, Grasses (allelopathically suppressed)

Cool Temperate Growing Tips for Sunflower

Recommended Varieties

  • Giant Russian
  • Mammoth Grey Stripe
  • Autumn Beauty
  • Italian White
  • Lemon Queen

Key Challenges

  • Shorter season - choose varieties that mature in 70-90 days
  • Late frosts can kill seedlings
  • Sclerotinia and downy mildew in wet years

Pro Tips

  • Grow in the warmest, sunniest spot in the garden
  • Start in pots indoors 2-3 weeks before last frost for a head start
  • Harvest heads before autumn rains begin to prevent mould

Harvesting Sunflower

When ready: For EDIBLE SEEDS: back of head turns from green to yellow-brown, petals have dried and fallen, seeds are plump and hard, head droops downward. For ORNAMENTAL cut flowers: harvest when first ring of outer florets opens, before fully open.

How to harvest: For seeds: cut head with 30cm of stem. Hang upside down in dry, airy place inside a paper bag or with cloth underneath to catch falling seeds. Alternatively, rub seeds out of head by hand once dry (wear gloves - rough). For cut flowers: cut stems early morning, place in water immediately.

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