Grow Cosmos in your garden

Cosmos plants and their flowers are simply beautiful. They are one of my favourite garden plants because they have masses of pretty, open flowers with a summery feel and an elegant look too. The foliage is pretty and feathery. Cosmos are great for cut flowers but they also provide vital food for pollinators, as the open flowers are packed full of pollen and nectar, essential food for butterflies and bees. Cosmos plants are really easy to grow from seed. They are quick to germinate and mature and one packet of seeds will provide dozens of healthy plants that you can use fill your garden with colour. Or if you don’t grow from seed, you can buy young plants or plug plants from the garden centre in late spring. The plants are mostly annuals that grow, flower and set seed in the same season and they have few pest issues and are pretty disease resistant too, what’s not to like?

cosmos seed
Cosmos provide vital food for pollinators. Image: Martin Mulchinock

Sun lovers

Cosmos originate from Mexico. This gives us lots of clues regarding their cultural needs. These sunny faced flowers are sun lovers. To give them the best conditions to grow, they need an open site and well-drained soil. Cosmos don’t like the cold. The annual plants are frost tender, which means frost will kill the plants; so if you grow from seed, don’t sow them too early. April is early enough and gives them time to grow on before you plant them outside after the last frost of winter. If you are buying plants, then wait until May and make sure you can keep your plants frost-free until it is safe to plant them outside. Cosmos grow pretty fast when they get going, so they need some TLC in terms of feeding. For masses of flowers use Flower Power Premium Plant Food, it will provide all the nutrients your plants need to flower all summer. It’s also important to water container grown plants, especially in hot weather. Plants in the border should be OK, but keep an eye on them, if they start to wilt in hot weather, soak the soil around them.

Growing from seed: step by step

One packet of seed will go a long way, but once you have fallen in love with cosmos you will want to share plants and flowers with everyone. Keep your seeds, seedlings and cosmos plants in a frost-free place while they grow.

  • Sow sparingly in small pots of seed compost from April and until June. Spread them out on the surface of the compost and cover with vermiculite, they need light to germinate so don’t bury them.
  • Water gently with slightly tepid water. They will germinate within a few days.
  • When they are large enough to handle, carefully tip them seedlings out of the pot, prise them gently apart and replant each one into small individual pots of young plant compost. This is called pricking out.
  • Keep them in a light and frost-free place until the last frost has passed (around June), when you can plant them outside into pots containers, beds and borders.
Cosmos flowers growing in pots

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