When to plant Aster in Subtropical Australia

Subtropical zone — applies to Brisbane, Gold Coast, Sunshine Coast, Coffs Harbour, Lismore and similar areas. Growing elsewhere? Temperate · Cool · Tropical · Arid.

Raise aster seedlings across July to January, transplanting once they are sturdy, and sow 5 mm deep for germination in 14–28 days. From sowing to flower takes 100–110 days, so a late-winter or spring start delivers colour through the warmer months. Space plants 20–30 cm apart in rows 20–30 cm, in full sun and free-draining soil. In subtropical gardens around Brisbane and the Sunshine Coast the challenge is humidity rather than cold, so airy spacing and good drainage matter more than frost protection. Asters give you long-lasting daisy flowers that hold well as cut blooms.

Sowing calendar — subtropical zone

Green months are your sowing window: July to January.

Growing notes

Asters are cheerful, reliable daisies, but in the subtropics they are prone to two humidity-driven problems that catch gardeners out.

The first is powdery mildew, which coats the leaves in a grey-white bloom during warm, still, humid spells. Space plants at the wider end of the 20–30 cm range, water at the base early in the day, and site them where morning sun dries the foliage quickly. Removing the lowest, most shaded leaves improves airflow around the crown.

The second is aster wilt, a soil-borne fungal disease that yellows and collapses plants from the base up. It builds in soil where asters grow year after year, so rotate them to a fresh bed each season and pull and bin, rather than compost, any plant that wilts and dies. Free-draining soil that never sits waterlogged after a Lismore storm goes a long way to preventing it.

Pinch the growing tips of young plants once to encourage branching and more flower stems. Feed lightly rather than heavily, as soft, over-fed growth is more susceptible to both mildew and pests, and stake taller varieties before summer storms knock them flat.

Aster at a glance

Common questions

Why do my asters get white powder on the leaves

That is powdery mildew, encouraged by subtropical humidity and still air. Space plants wider, water at the base in the morning, and site them in morning sun so the foliage dries quickly.

When can I plant asters in the subtropics

Raise seedlings across the long window from July to January and transplant them out once sturdy. From sowing they take 100–110 days to flower, so a late-winter or spring start gives colour through the warmer months.

Why do my asters suddenly wilt and die

This is often aster wilt, a soil-borne fungus that builds up where asters grow repeatedly. Rotate them to a fresh bed each year, ensure sharp drainage, and remove affected plants to the bin rather than the compost.

Should I pinch out asters

Yes, pinch the growing tip of young plants once to encourage branching and more flower stems. It also keeps plants bushier and less likely to flop in summer storms.

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