When to plant Cosmos in the UK

Sow seeds in trays or modules from mid-March to mid-April, 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 early April to early May. Pot them into small pots and keep them growing in a bright, frost-free place.

Acclimatise plants over 15 days before planting out, from early May to mid-May. 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 mid-May to early June, 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 mid-June to late October. 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.