Annual
Cosmos
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | Flowers in July | Flowers in August | Flowers in September | Flowers in October | ||||||||
| Plant | Plant in May | Plant in June | ||||||||||
| Looks good | Looks good in July | Looks good in August | Looks good in September | Looks good in October |
Overview
Cosmos is one of the easiest and most generous half-hardy annuals, growing into airy clumps of fine, feathery leaves topped with open, daisy-like flowers in white, pink and crimson. It is excellent for cutting, as the more you pick, the more it blooms. Try 'Purity' for clean white flowers, the compact 'Sonata' series for pots, 'Double Click' for frilly semi-double blooms, or 'Cupcakes', whose fused petals form shallow cups. Bees and hoverflies visit the open centres.
Where to grow cosmos
Full sun is the key. Plant cosmos in gaps in borders, a cutting patch, the back of a bed or large containers. Rich soil and heavy feeding produce lots of leaves and fewer flowers, so don't fuss over the ground.
Planting
Sow seed in modules on a windowsill or in a greenhouse in March or April, then prick out into small pots. Harden off and plant out from mid-May in the south, a few weeks later in northern or upland gardens, 30–45cm apart. Direct sowing in late May also works.
Care through the year
Spring
Pinch out the tips of young plants for bushier growth. Protect from late frosts with fleece if necessary.
Summer
Deadhead every few days or cut stems for the vase. Water in prolonged drought; tall types may need discreet stakes.
Autumn
Flowering continues until the first frost. Leave a few heads to set seed for next year.
Winter
Pull out blackened plants and compost them. Store saved seed in a paper envelope somewhere cool and dry.
Pruning
No structural pruning. Deadhead regularly, cutting back to a leaf joint or bud.
Propagation
Grow from seed each year. Saved seed from open-pollinated varieties often comes fairly true, and plants may self-seed in mild gardens.
Common problems
Slugs and snails love young seedlings, so plant out sturdy plants and protect them. Aphids sometimes cluster on shoot tips. Lack of flowers almost always means too much shade or too rich a soil.
Guides to the problems most likely to affect cosmos:
Something else wrong? Diagnose it by symptom.
Month-by-month reminders
Jobs for this plant come round in May and June. Each month page lists everything else worth doing in the garden at the same time.
Related plants
Sources
Botanical names follow Kew's Plants of the World Online; growing attributes were checked against the references below. Text is our own. See our editorial policy.