How to Grow Zinnias

How to Grow Zinnias from Seed

Zinnias are one of the easiest and most rewarding flowers to grow from seed. They’re fast-growing, heat-loving, and bloom generously all summer long, making them perfect for beginners. With just sun, warmth, and regular picking, zinnias will reward you with armfuls of colourful flowers.

When to Grow Zinnias in Australia

Zinnias are a warm-season annual and do not tolerate frost.

Best time to sow: Spring to early summer
Sow once all risk of frost has passed and soil has warmed
In most regions, this is September to December
In warm climates, sowing can continue into January

Zinnias thrive in heat and will grow quickly once temperatures stay above 18–20°C
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How to Sow Zinnia Seeds

You can grow zinnias by direct seeding into the garden or by raising seedlings first. Both methods work well.

Option 1: Direct Seeding (Easiest)

Direct seeding is simple and works best once the weather is warm.

Prepare a sunny spot with loose, well-drained soil
Sow seeds about 5–10 mm deep
Space seeds 20–30 cm apart (or thin later)
Water gently and keep soil moist until germination

Seeds usually germinate in 5–10 days in warm conditions.

Option 2: Raising Seedlings

Raising seedlings gives you more control early on and is useful in cooler areas.

Sow seeds into seed trays or small pots
Use a quality seed-raising mix
Lightly cover seeds and water in
Keep warm and bright (but not cold or wet)

Transplant seedlings once they are 5–8 cm tall and night temperatures are consistently warm. Avoid disturbing the roots too much.

Growing Conditions

Sun: Full sun (at least 6–8 hours a day)
Soil: Well-drained soil is essential
Water: Regular watering, especially when young
Airflow: Good spacing helps prevent disease

Zinnias dislike cold, soggy soil, so avoid planting too early in the season.

Ongoing Care

Water at the base of the plant rather than overhead
Remove spent flowers to encourage more blooms
Picking flowers regularly will keep plants productive
Taller varieties may benefit from light support in windy areas

With minimal care, zinnias will flower continuously through summer and into early autumn.