How to Grow


How to Grow Cosmos

Flowering abundantly for months in summer, cosmos add fabulous colour to sunny borders.
With ferny foliage and masses of big daisy-like flowers which are a magnet for pollinators,
the bright pink, red or white flowers are perfect for cutting, and last a long time in vases.

When your plants arrive

  • Unpack your plants immediately and check the compost to ensure it has not dried out in
    transit. Water with a fine spray, or sit the plants in a tray of shallow water if the compost is
  • Pot on plants as soon as possible (preferably within 24 hours) after they have had time to

Potting on and planting out plug plants

  • Handle each plant by the plug root ball, rather than the stem to avoid damage.
  • Pot each plug into a 7.5cm (3in) pot using a good multi-purpose compost or a
    container compost.
  • Grow on for a few weeks in a greenhouse or a bright, frost-free place, but avoid
    direct sunlight.
  • Keep moist but do not over-water. If very cold weather is forecast, cover with a layer
    of fleece.
  • Once there is no more danger of frost, the plants can be moved to their permanent
  • Harden off your plants before planting them out by placing the pots outside during
    the day and bringing them back in at night. After 7-10 days, the plants will be ready
    to plant out.

How to grow Cosmos from seed

  • Sow cosmos seeds indoors, 3mm deep in 9cm pots filled with seed compost.
  • Water the pots and place on a sunny windowsill or in a greenhouse to germinate.
  • When the seedlings have three pairs of true leaves, pinch out the growing tips to
    encourage bushy plants that will produce plenty of flowers.
  • Grow on until all risk of frost is past, then harden off as for plug plants, and plant

How to care for Cosmos

  • Plant in well-drained soil in full sun. If growing in containers, use a good
    multipurpose compost.
  • Feed container-grown plants fortnightly with a high-potash feed such as tomato feed
    once they start flowering. There’s usually no need to feed cosmos grown in the
  • Deadhead regularly to keep the plants producing flowers.
  • Most cosmos are annuals and will die naturally in autumn at the end of the flowering
    season. Once the plants have finished flowering, pull them up and compost them.

Pests and Diseases

Cosmos may be prone to the following pests and diseases. Read more about how to control
common plant pests and diseases here.


  • Slugs and snails


  • Generally disease-free

Cosmos Seedlings

Cosmos Garden Ready