where to grow cosmos
Soil type: Cosmos need good, well-drained soil to thrive.
Aspect & position: Cosmos need a position in full sun to flower productively
when to plant cosmos
Sow cosmos seeds undercover in March-April, or direct sow in May. Plant out seedlings once the frosts have passed in late May or June.
how to plant cosmos
sowing cosmos seeds undercover
Cosmos seeds can be sown undercover in March or April. The seeds are long and thin, so can be easily handled.
Use seed trays filled with good compost or Jiffy modules. Push two seeds about 3mm deep into each module. Water well and then place in a greenhouse or on a warm windowsill to help germination. If both seeds germinate, remove one of the seedlings a week later and leave the other one to grow on in splendid isolation.
Pot the seedlings on into larger pots when they are big enough to handle. Pinch out the growing tip of each stem when 3 pairs of true leaves have grown to encourage stems to branch and produce more flowers. Then plant out in late May or June once the risk of frosts has passed.
direct sowing cosmos seeds
Direct sow your cosmos seeds in May – the risk of frost should have passed by the time they emerge.
Prepare the soil before planting. Rake the patch until you have a fine, crumbly consistency. Space the seed about 5–8cm (2–3in) apart and water well.
About three weeks later, the seedlings should have popped up. At that point, you can thin them out to about 30cm (12in) apart. Pinch out the growing tip of each stem to encourage them to branch and produce more flowers.