When to plant Petunia in Temperate Australia

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

Raise petunias from seed in trays from August to December, transplanting seedlings out after the mid-October frost has passed, and barely covering the tiny seed at 3 mm. Germination takes 7–14 days and needs light, so press seed onto the surface rather than burying it. Plants flower in about 80–90 days and bloom through summer into autumn. Set transplants 25–40 cm apart with 25–30 cm between rows in full sun. In Sydney and Perth gardens petunias are a reliable warm-season bedding and container flower.

Sowing calendar — temperate zone

Green months are your sowing window: August to December.

Growing notes

Petunias are half-hardy warm-season flowers that carry beds, hanging baskets and pots through the temperate summer. Because the seed is dust-fine and needs light to germinate, most gardeners raise it in trays rather than sowing direct. Sprinkle seed on the surface of moist seed-raising mix, do not cover it, and keep it bright and warm until the seedlings appear in one to two weeks.

Transplant out only once frost has passed, around mid-October in temperate zones, into full sun and free-draining soil. The commonest failure is leggy, sparse plants with few flowers, usually from too little light or skipped pinching. Pinch out the growing tips of young plants to force bushy branching, and deadhead spent blooms so the plant keeps flowering rather than setting seed.

In humid coastal temperate gardens like Newcastle, botrytis grey mould can rot flowers and stems during wet spells. Improve airflow, avoid overhead watering late in the day, and remove any mouldy growth promptly. Feed container plants regularly, as petunias in pots are hungry and quickly go pale and flowerless when starved. Given sun, food and regular deadheading, they will bloom right through to autumn.

Petunia at a glance

Common questions

when do you sow petunia seeds in temperate Australia

Raise seed in trays from August to December and transplant seedlings out after the mid-October frost. This gives flowering plants through summer into autumn. The seed takes 7–14 days to germinate.

why are my petunia seeds not sprouting

Petunia seed needs light to germinate, so it must sit on the surface rather than be buried. Press the fine seed onto moist mix, do not cover it, and keep it bright and warm. Burying it is the most common reason for failure.

how do you make petunias bushy instead of leggy

Pinch out the growing tips of young plants to force side branching, and grow them in full sun. Leggy, sparse growth usually means too little light or no pinching. Regular deadheading keeps them compact and flowering.

why are my petunia flowers going mouldy

Grey mould, or botrytis, appears in humid, wet weather common on the temperate coast. Improve airflow, avoid watering the foliage late in the day, and remove affected flowers and stems promptly to stop it spreading.

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