Pink cosmos with tubular petals

How to grow cosmos

Find out all you need to know about growing cosmos, from sowing to planting in this easy Grow Guide.

A table displaying which months are best to sow, plant and harvest.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sow
Sow

Do not Sow in January

Do not Sow in February

Do Sow in March

Do Sow in April

Do not Sow in May

Do not Sow in June

Do not Sow in July

Do not Sow in August

Do not Sow in September

Do not Sow in October

Do not Sow in November

Do not Sow in December

Flowers
Flowers

Plant does not flower in January

Plant does not flower in February

Plant does not flower in March

Plant does not flower in April

Plant does flower in May

Plant does flower in June

Plant does flower in July

Plant does flower in August

Plant does flower in September

Plant does flower in October

Plant does not flower in November

Plant does not flower in December

Cut back
Cut back

Do not Cut back in January

Do not Cut back in February

Do not Cut back in March

Do not Cut back in April

Do not Cut back in May

Do not Cut back in June

Do not Cut back in July

Do not Cut back in August

Do not Cut back in September

Do not Cut back in October

Do Cut back in November

Do Cut back in December

Cosmos are sun-loving plants with a long flowering season. They fill borders with a profusion of flowers, ranging in colour from white through to pink, red and orange, in contrast with masses of feathery foliage. Shorter varieties also look good in containers and all cosmos make fantastic cut flowers. The simple open flowers are guaranteed to brighten up any garden well into autumn, and pollinators like them just as much as gardeners do.

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How to grow cosmos

Grow cosmos in moist but well-drained soil in full un. Deadhead to prolong flowering and lift in autumn, after the first frosts. Save seed from spent blooms to sow the following season.

More on growing cosmos:


Where to grow cosmos

Pink cosmos
Pink cosmos

Cosmos are native to Southern and Central America and therefore need to be planted in a warm, sunny spot. Soil should be free-draining.


How to plant cosmos

Potting on cosmos seedlings
Potting on cosmos seedlings

Sow seed in early spring directly into the soil where you want your cosmos to grow, or into small pots or modules filled with free-draining seed compost. If growing in pots, pot on when the seedlings are large enough to handle. Plant out in late April/May after the danger of frost has passed.

Watch Monty Don plant out cosmos for a late summer display:


How to care for cosmos

How to grow cosmos - how to care for cosmos
How to grow cosmos – how to care for cosmos

Once your seedlings have formed 2-3 pairs of leaves, you can 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 and fed with a liquid fertiliser. When deadheading, cut the stem back to the first leaf beneath the flowerhead.

The perennial chocolate cosmos varieties will need winter protection. Place them in pots until they’ve finished flowering, then shelter over winter in a frost-free place until spring.

Here, Monty Don explains how deadheading spent flowers will keep them blooming for as long as possible:


How to propagate cosmos

Collecting seed from cosmos seedheads
Collecting seed from cosmos seedheads

You can collect seed from flowering cosmos and save for next year. Or if you’re growing chocolate cosmos, you can divide the tubers when you lift the plants for storage over the winter months.


Growing cosmos: problem solving

Planting out cosmos seedlings
Planting out cosmos seedlings

Cosmos are pretty much trouble-free to grow, apart from the threat of slugs and snails when seedlings are young and tender.


Great cosmos varieties to grow

Cosmos 'Sonata White'
Cosmos ‘Sonata White’
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