How to Grow Cosmos in Australia
A warm-season flower crop for the home garden
Growing Cosmos at home is well within reach for most Australian gardeners, and this guide walks you through every step. They are rated beginner to grow. Saves ~$8-15/bunch on cut flowers, self-seeds every year so you never buy seed again.
This guide covers when to plant Cosmos in your region, the position and soil they like, how to sow and space them, day-to-day care, the pests and diseases to watch, and how to harvest and store your crop.
When to Plant in Your Region
Cosmos are a warm-season crop, frost-tender and needs a frost-free run. In subtropical South-East Queensland they are sown in September, October, November, December, January and February. Timing shifts with your climate, so choose your region below for a local calendar.
Varieties to Try
Sensation Mix
The classic tall cosmos (1.2m). Large single blooms in white, pink and crimson. Self-seeds freely. The standard.
Try: Yates, Mr Fothergill's, Eden Seeds, Bunnings
Cosmic Orange (Sulphureus)
Compact (60cm) with semi-double bright orange blooms. Heat-loving, different species. Brilliant for hot climates.
Try: Mr Fothergill's, Eden Seeds, Yates
Double Click Mix
Double and semi-double blooms like small dahlias. Tall. Stunning cut flowers. More variety than Sensation.
Try: Mr Fothergill's, Eden Seeds
Position and Soil
Give Cosmos full sun (at least 6 hours a day). They do best in free-draining soil with a pH around 6 to 7. Dig through plenty of compost before planting, and mulch to hold moisture and keep weeds down. They grow happily in a pot of 25cm+, which makes them a fine choice for balconies and courtyards.
Sowing and Spacing
Sow seed on the surface, barely covered. Thin or space plants to about 30 cm apart. Seedlings usually appear in around 7 days, fastest when the soil is between 18 and 28 degrees.
One of the easiest and most rewarding annual flowers. Feathery foliage with daisy-like blooms in white, pink, red and orange. Attracts butterflies, bees and beneficial insects including hoverflies and lacewings. Thrives in poor soil (too much fertiliser produces leaves not flowers). Direct sow after frost. Deadhead to extend flowering. Self-seeds freely for return crops each year.
Care
Water consistently, roughly 3 L per plant every 3 days in warm weather, less in cool or wet spells. Feed every few weeks through the growing season with a balanced organic fertiliser, and keep mulch topped up.
Pests and Diseases
Keep an eye out for Aphids and Thrips. The main diseases to watch are Powdery mildew and Aster yellows. Good spacing, watering at the base rather than over the leaves, and crop rotation prevent most problems. See our Pest and Disease Guide to identify and fix any issue.
Harvesting and Storage
Cosmos are typically ready to harvest in around 60 days (about 2 months). Cut flowers last 5-7 days in a vase. Harvest when buds just open. Save seed from dried heads.
In the Kitchen
In the kitchen, cosmos are good petals used as an edible garnish, flowers added to salads for colour and blooms used in floral arrangements. Nutritionally: attracts beneficial insects including lacewings and hoverflies and supports pollinator populations.
Companion Planting
Cosmos grow well alongside Tomato, Beans, Capsicum, Cucumber and Marigold. Our Companion Planting Guide has the full pairings.
Track Your Cosmos Growing
Add cosmos to your garden in the Planting Season app and get reminders for planting, care and harvest, tuned to your region.
Open the App →Frequently Asked Questions
When should I plant Cosmos in Australia?
Cosmos are a warm-season crop. In subtropical regions like South-East Queensland they are sown in September, October, November, December, January and February. Timing changes with your climate, so use the calendar above for your region.
How long does Cosmos take to grow?
Cosmos are generally ready to harvest in around 60 days (about 2 months).
Can I grow Cosmos in a pot?
Yes. Cosmos grow well in a container of 25cm+ with free-draining mix and regular watering.
How much sun does Cosmos need?
Give they full sun (at least 6 hours a day) for the healthiest growth and best harvest.
See also: Cosmos in the Plant Library
