When to plant Cosmos in London

Sow seeds in trays or modules from 18th February to 14th March, using 0.5 cm of fine compost. Keep them at 18–21 °C and just moist, not wet.

Move seedlings on when they are large enough to handle, from 4th March to 11th April. Pot them into small pots and keep them growing in a bright, frost-free place.

Acclimatise plants over 15 days before planting out, from 4th April to 18th April. 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 18th April to 5th May, spacing plants 30 cm apart. Water in thoroughly straight after planting and protect young plants from slugs and late cold snaps if needed.

Remove fading flowers regularly from 18th May to 10th 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.