- Home
- How to
- Grow plants
- How to grow cosmos
How to grow cosmos
- BBC Gardeners' World Magazine
Published: Wednesday, 27 May 2026 at 10:52 am
Find out all you need to know about growing cosmos, from sowing to planting in this easy Grow Guide.
JanFebMarAprMayJunJulAugSepOctNovDecSowyes**yesFlowersyesyesyesyesyes**yesCut Backyes**yes
Save
- Share on facebook
- Share on twitter
- Share on pinterest
- Share on whatsapp
- Share on blogger
- Email to a friend
This article has been checked for horticultural accuracy by Oliver Parsons.
Ad
Cosmos are sun-loving plants with a long flowering season, from May to September. They fill borders with a profusion of flowers, ranging in colour from white through to pink, red and orange, and they have masses of feathery foliage. Cosmos is considered a birth flower for October, and is associated with order and balance.
Shorter varieties look good in containers and all cosmos make fantastic cut flowers. Their simple open flowers are guaranteed to brighten up any garden well into autumn - and pollinators like them just as much as gardeners do.
There are both annual and perennial types of cosmos but they are both grown as hardy annuals in the UK as they don't survive our winters. However, if you leave them to develop seeds, they will self-seed around the garden or you can collect seed to sow the following spring.
Where to grow cosmos
Pink cosmos
Cosmos are native to Southern and Central America, so need to be planted in a warm, sunny spot, in free-draining soil. It works well when planted into gaps in a sunny border, and can also be grown in pots.
How to plant cosmos
Potting on cosmos seedlings
Sow cosmos seeds in early spring directly into the soil where you want them to grow, or into small pots or modules filled with free-draining seed compost. If growing in pots, pot on seedlings when they are large enough to handle. Plant out in late April, May or early June after the danger of frost has passed.
Watch this video, below, to see Monty Don plant out cosmos for a long summer display.
How to care for cosmos
Deadheading cosmos
Once your seedlings have formed 2-3 pairs of leaves, pinch out the growing tips to produce bushier plants with more flowers.
Taller varieties may need staking, otherwise all varieties will flower for a long period if deadheaded regularly. When deadheading, cut the stem back to the first leaf beneath the flower.
The tender perennial chocolate cosmos varieties will need winter protection. Grow them in pots, then when they've finished flowering shelter them over winter in a frost-free place until spring.
In the video below, Monty Don explains how deadheading spent flowers will keep them blooming for as long as possible.
How to propagate cosmos
Collecting seeds from cosmos seedheads
You can collect seeds from flowering cosmos and save them for sowing next year. Or if you're growing chocolate cosmos, divide the tubers when you lift the plants for storage over winter.
Pests and diseases
Planting out cosmos seedlings
Cosmos are pretty much trouble-free to grow, apart from the threat of slugs and snails when the seedlings are young. You may find aphids on new growth in spring and summer – these are usually fine to leave as ladybirds and other predators will find them.
Great cosmos varieties to grow
Cosmos Sonata White
Ad
- Cosmos Sea Shells – with pale, fluted petals – looking like a sea shell – it's a great planting partner for dark-flowered dahlias and chrysanthemums
- Cosmos bipinnatus Sonata White – a compact cosmos, good for growing in containers. Masses of pure-white, single, saucer-shaped flowers appear throughout summer
- Cosmos bipinnatus Fizzy Pink – with strong flower colours from white to carmine, this variety is good for cutting or growing in pots
- Cosmos 'Gazebo Red' – a medium-sized, bushy, early-flowering variety of cosmos, with large, velvety red blooms
- Cosmos atrosanguineus – the chocolate cosmos is a tender perennial from Mexico. The dark cocoa-coloured flowers have a faint scent of vanilla and chocolate. It grows from tubers, unlike other cosmos, and should be treated like a dahlia or canna lily, lifting to overwinter indoors or mulched heavily in autumn.
Frequently asked questions
My cosmos are very tall and sturdy, so why do they have no flowers?
If your cosmos are tall, strong and bushy but without blooms, they may have been overfed with nitrogen-based fertiliser or grown in soil that is too fertile. This can cause cosmos to grow foliage at the expense of flowers. Cosmos flower best when planted in full sun and in free-draining, average garden soil. Plants in shade will also struggle to flower. Pinching out cosmos plants should lead to more blooms.
When do I pinch out my cosmos?
The best time to pinch out the tops of cosmos seedlings is when they have grown three sets of true leaves (fern-like leaves). This will encourage plants to branch out and become bushier. It should also lead to more flower production.
My cosmos are leggy. How do I prick them out?
Don’t sow cosmos too early in the year, when sunlight is weak, and make sure they get plenty of light to avoid leggy growth. But if your cosmos seedlings have already become leggy, don’t worry. Just prick out and pot on into a slightly larger container, planting the seedlings a little deeper than they were. If you haven’t already pinched out the tops, do that now to encourage bushier growth.
Loading...
Ad
Ad
Don't miss out this Winter
Enjoy expert advice on what to plant and grow this winter, and how to prepare your plot for the year ahead. Enjoy, 6 months for just £31.99
Great gardening savings - straight to your inbox
Sign up to the BBC Gardeners’ World offers newsletter for exclusive deals, seasonal savings, and early access to special promotions.
Loading...
Ad
Loading...
Loading...