Cosmos are as brilliant in the garden as they are in the vase. Plant expert Graham Rice chooses his favourite cosmos varieties to grow, and gives advice on sowing and growing them. Photographs by Jason Ingram
There are about 30 species of cosmos – both annuals and perennials. A recent trial at RHS Garden Wisley of almost 90 annual cosmos made it clear what valuable plants they are in borders, in pots and as cut flowers.
The familiar annual, Cosmos bipinnatus,is a vigorous plant that reaches from 60cm to 3m, with stout upright stems carrying fresh green, feathery foliage. From midsummer into autumn, large golden-centred daisies open in a wide range of white, pink and rich-red shades. In 2017 the first yellow-flowered variants were introduced.
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Cosmos bipinnatus flowers can be single, double, semi-double or quilled. The petals may be edged or streaked in darker shades or feature rings around the golden eye.
Annual cosmos are ideal for growing among shrub roses or perennials. The taller types are good at the back of beds or as a temporary screen. The shorter varieties are better for the middle or front of a border and are excellent for pots.
The perennial Cosmos sulphureus has orange or yellow flowers and the popular and tender tuberous chocolate cosmos (Cosmos atrosanguineus), has chocolate-coloured and scented flowers. Both are usually grown as an annual in the UK.
Jump to
- How to choose cosmos
- How to grow cosmos
- When to pinch out cosmos
- The best cosmos for containers
- How to sow cosmos seeds
- Where to grow cosmos
- The best cosmos to grow
The best cosmos for containers
- The British-bred Apollo Series in carmine, white and pink is the best choice for containers. ‘Sea Shells’, with each petal rolled into a tube, is striking and especially good in vases, but on the Wisley evidence it deteriorated badly; try the shorter Hummingbird Series instead.
How to grow cosmos
When to pinch out cosmos
Once the seedlings have formed two or three pairs of leaves, pinch out the growing tips to produce more bushy plants that will go on to produce more flowers.
When to sow cosmos seeds
- Sow cosmos seeds in a seed tray or modules in April, in a greenhouse or on a sunny windowsill. Cosmos can also be sown directly outside where they are to flower, but wait until the middle of May.
- Transplant the young seedlings to individual 7cm pots.
- Plant outside in late May or June.
- Before planting out, acclimatise plants to the outdoors by hardening them off first. Space the plants 30-60cm apart, depending on their eventual height.
Read our detailed guide to sowing seeds.
Where to grow cosmos
Grow cosmos in full sun, in a sheltered spot, in well drained soil.
Caring for cosmos
Regular deadheading is crucial to maintaining a continuing display of flowers into September and even October. Both Cosmos bipinnatus and Cosmos sulphureus are good as cut flowers; pick them when the petals are starting to open (but are not fully open) and change the water every day. Feed cosmos growing in pots with a liquid feed every two weeks.
Support may be necessary: smaller cultivars can be supported with brushwood, while taller cultivars need the more solid support of canes and twine.
Mildew may prove a problem if the plants are not thinned out or if they are grown in very sheltered situations; free air movement is the best preventative measure in this case.
The best cosmos to grow in 2024
Cosmos bipinnatus ‘Antiquity’
A shorter, newcomer cosmos variety. The unusual and beautiful single flowers fade from a beautiful rich red to paler ‘antique’ tones as they age, creating a two-tone effect and with a variety of flower colours at any one time on the plant. As Cosmos bipinnatus ‘Antiquity’ it’s a shorter variety, it doesn’t need staking and is ideal for both borders and containers. Deadhead when the flowers begin to look ragged, or cut regularly for cut flowers – the blooms should last for 10 days in a vase. A beautiful and easy flower to grow from seed.
Height 60cm.
Cosmos bipinnatus ‘Cupcakes White’
For something a bit different, Cosmos bipinnatus ‘Cupcakes White’ has unusual, cupped flowers with pure white petals that are fused into large bowl-shaped flowers that are reminiscent of paper cupcake cases. Some of the flowers may also be pink-tinted or may have split or semi-double flowers. ‘Cupcakes White’ was Voted ‘People’s Favourite’ by the visitors to the cosmos trial at Wisley. Grow Cosmos bipinnatus ‘Cupcakes White’ in a border or in a container. ‘Cupcakes Mixed’ has a balance of white and pink shades.
Height 1.2m.
Cosmos bipinnatus ‘Candy Stripe’
Tall, rather leafy cosmos plants with fresh-green foliage carry single, long-stemmed white flowers, each vividly edged with bright carmine. Some flowers are almost fully white, the variability in the markings adds to the appeal.
Height 2m.
Cosmos bipinnatus ‘Double Click Rose Bonbon’
Double-flowered cosmos forms can be disappointing. This is the pick from Wisley because although there were very few doubles, the singles and fluted flowers matched perfectly in colour to create a fascinating, rosy-pink blend.
Height 1.8m.
Buy Cosmos bipinnatus ‘Double Click Rose Bonbon’ from Thompson & Morgan
Cosmos bipinnatus ‘Rubenza’
Deep-red, scarlet or deep-pink single cosmos flowers on tall but prolific plants. Rich colouring and good with silver foliage, the flowers age harmoniously but eventually need regular deadheading.
Height 1.5m.
Buy Cosmos bipinnatus ‘Rubenza’ from Thompson & Morgan
Cosmos bipinnatus ‘Xanthos’
Very pretty cosmos that is a Fleuroselect Gold Medal winner. The small, mostly single, primrose-yellow flowers have a neat, white ring around the golden eye; a few flowers have extra petals and there are a few white flowers.
Height 1m.
Buy Cosmos bipinnatus ‘Xanthos’ from Crocus
Cosmos bipinnatus ‘Cosimo Red-White’
Like a shorter version of ‘Candy Stripe’, the striking plants are best early and mid-season, while the compact foliage allows the flowers to bloom unhidden. Cruder in colour than the softer, but taller, Cosmos ‘Capriola’.
Height 60cm.
Buy Cosmos bipinnatus ‘Cosmimo Red-White’ from Kings Seeds
Cosmos bipinnatus ‘Apollo Carmine’
One of the best cosmos in the Wisley display, short plants carry rich, carmine single flowers that hold their colour well and fade harmoniously into pinkish tones. Good flower shape and size, ideal in large containers.
Height 60cm.
Cosmos bipinnatus ‘Apollo Pink’
Nicely rippled, rose-pink single cosmos flowers face upward from uniformly neat plants, the colour hardly fading before the petals start to drop. An improvement on the similar, but now unacceptably variable, ‘Sonata Pink’.
Height 60cm.
Buy Cosmos bipinnatus ‘Apollo Pink’ from Hayloft
Cosmos bipinnatus ‘Apollo White’
Large, flat, upward-facing, pure-white flowers on plants of uniform height, Cosmos ‘Apollo White’ flowers consistently from June until well into the autumn. The Apollo Series is the new standard in short cosmos.
Height 60cm.
Buy Cosmos bipinnatus ‘Apollo White’ from Lazy Flora
Cosmos sulphureus ‘Brightness Red’
Semi-double flowers in vivid reddish orange, with a few orange-flowered plants mixed in. Flowers are sparse at first but prolific later on, and open at various heights on the plant, not only at the top. Seeds are currently hard to track down – it is mostly available as part of a mix.
Height 50cm.
Buy Cosmos sulphureus ‘Brightness Mixed’ from Thompson & Morgan
Cosmos bipinnatus ‘Capriola’
My favourite, the white flowers are exquisite with their unique pattern: each petal on this cosmos is boldly tipped and edged in magenta pink with a similar ring around the eye. Sadly, it can be variable, and there are some ‘off’ types.
Height 1.2m.
Buy Cosmos bipinnatus ‘Capriola’ from Thompson & Morgan
Cosmos bipinnatus ‘Veloutte’
Perhaps the most dramatic cultivar, white flowers are tipped and streaked in reddish carmine, though some flowers are almost entirely white and some completely carmine. Eventually this cosmos fades to parched pink, when deadheading is necessary.
Height 1m.
Buy Cosmos bipinnatus ‘Veloutte’ from Dobies
Cosmos bipinnatus ‘Rosetta’
A new medium-height cultivar with large, mainly semi-double flowers striped in lavender pink and blushed white. Very pretty, early, long-flowering and prolific cosmos, but, strangely, its flowers all face in different directions.
Height 1.2m.
Buy Cosmos bipinnatus ‘Rosetta’ from Thompson & Morgan
Cosmos bipinnatus ‘Versailles Dark Rose’
The best of the tallest types of cosmos; the large, single, rich-rose flowers have a dark-red ring around the golden eye. Too tall and leafy for many gardens, but good at the back of the border and for cutting. It is currently hard to track down seed.
Height 2.5m.
Find Cosmos bipinnatus ‘Versailles Dark Rose’ through the RHS<
Cosmos sulphureus ‘Carioca’
Wonderful, glowing-orange single cosmos flowers on plants with appealingly open growth, slow to start but prolific later. Lovely interplanted among dark-leaved cannas or dahlias for contrast in habit and colour. It is currently hard to track down seed.
Height 1m.
Find Cosmos sulphureus ‘Carioca’ through the RHS
You can find more information on hardiness ratings here.
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How to choose the best cosmos
The best varieties of cosmos are usually only available as seeds.
Cosmos seed is not a high-value crop, so time is rarely spent ensuring top quality in plants grown from seed of older cultivars that do not attract high prices. This was borne out in the Wisley display, where old cultivars, such as ‘Sensation Mixed’, ‘Purity’, ‘Sea Shells’, ‘Dazzler’, ‘Daydream’ and ‘Versailles Tetra’, flowered late and sparsely, often on uncomfortably tall plants. I would not recommend them.
Instead, I would recommend new and recent introductions where a slightly higher price translates into better quality. The one group where this approach fails is the double-flowered Double Click Series, where not one cultivar consistently produces double flowers.
Recent introductions also bring us new colours and patterns. Single-flowered, single-coloured Cosmos bipinnatus ‘Rubenza’ in deep red, and Cosmos bipinnatus ‘Xanthos’ and Cosmos bipinnatus ‘Lemonade’ in lemon yellow, stand out. Of the striped types, Cosmos bipinnatus ‘Velouette’ in white and dark red is dramatic. Cosmos bipinnatus ‘Capriola’ is my favourite, with white petals edged in pink and prolific flowers on 1.2m plants.