
Cosmos bipinnatus
A half-hardy annual grown for long-lasting, daisy-like flowers. In the UK it does best in a sunny, sheltered spot with free-draining soil, and it flowers freely from summer into autumn if you keep it deadheaded.
Step-by-step instructions for growing Cosmos
Sow seeds in trays or modules from 3rd February to 27th February, using of fine compost. Keep them at and just moist, not wet.
Move seedlings on when they are large enough to handle, from 1st March to 15th March. Pot them into small pots and keep them growing in a bright, frost-free place.
Acclimatise plants over 15 days before planting out, from 6th March to 20th March. Put them outside in the daytime at first, then leave them out for longer each day so they do not check in cold weather.
Plant into free-draining soil from 3rd April to 20th April, spacing plants apart. Water in thoroughly straight after planting and protect young plants from slugs and late cold snaps if needed.
Remove fading flowers regularly from 11th May to 12th November. This stops the plant setting seed too early and keeps it producing flowers until the autumn frosts. Tie in taller stems if the plants get blown about, and water during dry spells.
Tap a plant to see why it works (or doesn't) with Cosmos.
Companion planting can deter pests, improve pollination, and make better use of space. Some plants confuse pests or attract beneficial insects; others improve soil or offer shade to neighbours that need it.
Popular varieties of Cosmos to consider
Tall, open plants with large single flowers in mixed colours. A very common bedding and cutting strain in UK catalogues.
Tall white-flowered plants with good stems for cutting. Reliable in a sunny border.
Distinctive tubular petals and strong colour range. Good for a lighter, airy planting effect.
A shorter, compact type suited to pots and front-of-border planting. Useful where space is limited.
See how Cosmos timing shifts in other towns with different frost dates.