When to plant Zinnia in Cool Australia

Cool zone — applies to Hobart, Canberra, Ballarat, Orange, Armidale and similar areas. Growing elsewhere? Temperate · Subtropical · Tropical · Arid.

Sow zinnias direct from September to December, once frosts have finished and the soil is warm. These half hardy annuals resent cold, so in Hobart and Canberra it pays to wait until late spring rather than rushing an early sowing. Seed germinates quickly in warm ground, taking 6–21 days, and dislikes being transplanted, so direct sowing suits it well. Sow 6 mm deep and thin to 20–40 cm apart in rows of 30–45 cm. Expect a long run of cut flowers from around 100 days, right through summer and into autumn.

Sowing calendar — cool zone

Green months are your sowing window: September to December.

Growing notes

Zinnias are a warm-season flower, and in the cool zone your window is the frost-free stretch of summer, roughly November to April in Ballarat or Orange. Sowing too early, into cold, wet soil, is the single most common mistake; the seed rots or the seedlings sulk and never recover. Hold your nerve until nights are mild and the ground has warmed, and germination is fast and even.

The main disease to watch is powdery mildew, which coats the leaves in a grey-white film late in the season, especially where air is still and evenings are damp. Space plants at the wider end of the range for airflow, water at the base rather than over the foliage, and choose a sunny, open spot. Removing the lowest leaves also helps air move through the planting.

Zinnias are cut-and-come-again flowers, so the more you pick, the more they produce. Cut or deadhead regularly and the display keeps building until the first autumn frost knocks them down. They ask little beyond sun, warmth, and moderate water, making them one of the most rewarding annuals for a cool-zone summer garden.

Zinnia at a glance

Common questions

when to plant zinnias in Canberra

Wait until frosts have passed and the soil is warm, which usually means late spring through early summer, from September to December. Rushing an early sowing into cold Canberra soil often ends in rotted seed or stalled seedlings.

should you start zinnias indoors or direct sow

Direct sowing is best, as zinnias dislike root disturbance and resent transplanting. Sown into warm soil they germinate quickly and grow away strongly without the check that transplanting causes.

how do you stop powdery mildew on zinnias

Improve airflow by spacing plants generously, water at the base rather than over the leaves, and grow them in a sunny, open position. Removing the lowest leaves also helps keep the foliage dry and mildew-free.

how do you get more flowers from zinnias

Pick or deadhead often, as zinnias are cut-and-come-again and respond to regular harvesting with more blooms. Kept cut, they flower from around 100 days right through to the first autumn frost.

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