How to Grow Cosmos

Cosmos are a flower growers best friend. They are so delicate and beautiful, and come in such a variety of shapes and sizes. They are very easy to grow and produce loads of flowers throughout the summer. So, if you’re new to growing flowers and don’t know where to start, give these guys a whirl!

Cosmos are half hardy annual flowers, which means they need a nice, consistently warm temperature to germinate and grow, and don’t like being too cold. They won’t like a frost one bit! If a flower is an annual, it means it will germinate, grow, bloom and die, all in one year. And it won’t come back year on year. With this in mind, April is a good time to start sowing cosmos.

You will need a seed tray, or some pots, some seed, and some compost. Fill your pots up with compost to the top, and firm it down. Make a little hole, with a pencil in the middle of the pot, and pop your seed in. Cosmos seeds and fairly big so aren’t too tricky to handle. Make sure your hole isn’t too deep, maybe just a few centimetres. Cover the seed over with some compost and give it a water. Easy peasy! You can put your pots on a warm windowsill in the house until they pop up.

If you have a greenhouse, you can transfer your seedlings out to there where they are a bit bigger and stronger, but don’t worry if you don’t. When they have grown on a little, you need to harden your plants off. This means, get them used to being outside, so it’s not too much of a shock when you plant them in the garden. So, when they are bigger, put them outside in their pots for the day, and bring them in at night again. You need to do this for at least two weeks before you plant them in the garden. You will be able to plant them outside when the last frost is gone (usually at the end of May in Yorkshire!).

When you plant your cosmos out in the garden, make sure you give them some support. You can do this with either netting, or tying them to a cane. You will need to plant your plants about 25cm apart, as they grow quite big. When they start to flower, make sure you cut the flowers regularly and deadhead as much as you can. This will encourage the plant to grow more flowers, instead of going to seed.

The varieties we are growing this year are; ‘Purity’, ‘Double Click’ and ‘Cosmic Red’.