When to plant Zinnia in Subtropical Australia

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

Sow zinnias direct across a long warm-season window, from July to December and again in January and February, dropping seed 6 mm deep straight where they are to flower. They dislike root disturbance, so direct sowing beats transplanting. Seed germinates in 6–21 days depending on warmth, and plants bloom in around 100 days. Thin or space them 20–40 cm apart in rows 30–45 cm wide, in full sun. Zinnias love subtropical heat, giving Brisbane and Gold Coast gardens bold, long-lasting cut flowers right through the warmer months.

Sowing calendar — subtropical zone

Green months are your sowing window: July to February.

Growing notes

Zinnias are a heat-lover's flower, which makes them well suited to subtropical summers. They flower fast from seed, come in almost every colour, and the more you cut them the more they bloom. Sow small batches every few weeks for continuous colour from mid-winter through to autumn.

The one real enemy here is humidity, and the failure mode is powdery mildew. In the muggy wet around the Sunshine Coast and Coffs Harbour, leaves develop a grey-white dusting, then brown and die from the base up. Reduce it by giving plants room to breathe, watering at soil level rather than over the foliage, and choosing mildew-resistant varieties where you can. Morning sun that dries the leaves quickly helps a lot.

A few other tips:

• Pinch out the growing tip of young plants once they have several leaf pairs to force bushier, more productive growth.
• Deadhead or cut flowers regularly, as any seed set slows new blooms.
• Watch for caterpillars and spider mites in hot dry spells, and hose mites off early.

Stake taller varieties, since summer storms can flatten a heavily flowering row overnight.

Zinnia at a glance

Common questions

When should I plant zinnias in Brisbane?

Sow direct across the warm season, from July through to December and into January and February. Zinnias thrive in subtropical heat and germinate in 6–21 days. Successive small sowings give continuous flowers for months.

Why do my zinnias get powdery mildew?

Humid subtropical air is the cause. Crowded plants and wet foliage let the grey-white fungus take hold. Space plants well, water at the base, give them morning sun, and choose resistant varieties to reduce it.

Should I start zinnias in pots or sow them direct?

Sow direct where possible. Zinnias resent root disturbance and often sulk after transplanting. Dropping seed 6 mm deep straight into a sunny bed gives the strongest plants.

How do I get more zinnia flowers?

Pinch out the tip of young plants to make them bushier, then cut or deadhead often. Removing flowers before they set seed keeps the plant producing. The more you pick, the more it blooms.

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