When to plant Aster in Temperate Australia

Temperate zone — applies to Sydney, Melbourne, Adelaide, Perth, Newcastle and similar areas. Growing elsewhere? Cool · Subtropical · Tropical · Arid.

Raise asters from seedlings sown in spring and early summer from August to December, transplanting once frosts have finished. Sow at about 5 mm deep and allow 14–28 days for germination in warm conditions. These half-hardy flowers take around 100–110 days to bloom, so a spring sowing delivers a display through late summer and autumn just as many other flowers fade. Space plants 20–30 cm apart in both directions in a sunny, open bed with good air movement. Asters are a reliable cut flower for temperate gardens around Sydney, Melbourne and Adelaide, giving colour well into the cooler months.

Sowing calendar — temperate zone

Green months are your sowing window: August to December.

Growing notes

Asters earn their keep by flowering late, carrying colour into autumn when the summer annuals are winding down. They make excellent cut flowers and draw bees and butterflies to the garden. As half-hardy plants, they cope with cool nights but resent hard frost while young, which is why the August to December window keeps them clear of the frost-prone end of the temperate year.

The defining failure with asters is fungal disease. In crowded, still, humid conditions they are prone to powdery mildew and fusarium wilt, which yellows and collapses whole plants. The best defence is spacing and airflow: give each plant its full 20–30 cm, water at the base rather than over the leaves, and avoid planting asters in the same bed year after year, which lets soil-borne wilt build up. Rotate their position around the garden.

In a wet Melbourne summer, mildew can whiten the foliage badly; improve airflow, remove the worst leaves and avoid overhead watering late in the day. Pinch out the growing tips of young plants once or twice to build bushier, more floriferous plants, and stake the taller cutting types before they flop under the weight of bloom. Deadhead regularly and the display keeps coming until the cold sets in.

Aster at a glance

Common questions

when do asters flower in Australia

Asters sown in spring from August to December flower from late summer into autumn, taking around 100–110 days from sowing. This late display is one of their main attractions, filling the gap as summer annuals fade.

why are my aster leaves turning white

That is powdery mildew, common in crowded, humid conditions. Improve airflow by spacing plants their full 20–30 cm, water at the base rather than the foliage, and remove badly affected leaves to slow it down.

why did my asters suddenly wilt and die

Sudden collapse often points to fusarium wilt, a soil-borne fungus. Avoid replanting asters in the same bed each year, rotate their position, and improve drainage. There is no cure once a plant wilts, so prevention through rotation is key.

how far apart to plant asters

Space asters 20–30 cm apart in both directions. Generous spacing is not just about size; it improves airflow and is your main defence against the mildew and wilt that plague crowded plantings.

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