When to Plant Sunflower in Cairns, Tropical Guide

Sow March to September. Right now in September you can sow.

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

This Sunflower 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.

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.

Planting Calendar for Tropical

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

S = Seed Tray   T = Transplant   D = Direct Sow

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Current Growing Conditions

Soil temperature: 21.4°C (optimal range: 15–35°C) ✓ Ready to plant

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

How to Grow Sunflower in Tropical Australia

When to Plant

Sow April-August (dry season). Wet season growing risks head rot and Alternaria. Almost year-round possible but dry season is vastly better.

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)

Tropical Growing Tips for Sunflower

Recommended Varieties

  • Mammoth Russian/Giant Russian (edible seed)
  • Sunspot (dwarf, edible)
  • Autumn Beauty (ornamental, branching)

Key Challenges

  • Alternaria leaf blight in humid conditions
  • Head rot in wet weather
  • High insect pressure

Pro Tips

  • Time seed maturation for dry weather
  • Choose fast-maturing varieties (60-70 day types)
  • Space widely for air circulation

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.

Common Sunflower Pests in Tropical Zones

Aphids and Leaf Spots, risk: MODERATE (score: 45/100)

Organic prevention: Early planting so heads develop before peak moth activity (mid-late summer). Destroy infected heads after harvest. Clean up all crop residue.

View all pest alerts →

Where to next

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

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Common Questions About Sunflower

When do you plant sunflower in Australia?

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

Does sunflower grow all year round in Cairns?

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

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.