By Holly Reaney
Cosmos is a true garden favorite. Coming in a wide range of colors, they add instant wow-factor to the border and pack a punch in a pot.
As if their beauty wasn't enough to make you fall in love with these beautiful blooms, their pollen-rich flowers are a favorite with wildlife. Bees especially like cosmos making it a great addition to the garden, as it supports this vital pollinator.
Cosmos is best grown from seed and can be sowed any time throughout spring. 'The beauty of growing cosmos from seed, is that you can get so many' says Monty Don in a recent Gardener's World video. This makes it a really easy and affordable way to fill your borders with a stunning floral display come summer.
How to grow cosmos
When it comes to growing cosmos from seed you have two options. You can grow them in modules in a greenhouse or plant them directly out in the garden. There are benefits to both.
Growing cosmos in modules gives you more control over your blooms. Keeping them off the ground and undercover will also protect the delicate seedlings from slugs and harsh weather. Plus, since you are starting your plants off indoors (whether that's in a greenhouse or on a windowsill), you are able to start planting earlier (in early spring) so will have a well established, flowering plant by early summer.
See: Monty Don’s tips on getting the perfect lawn – and the mistakes you're making
If you are starting your cosmos in the greenhouse, then it is essential to harden them off. Thankfully, hardening off is very important and very easy. Simply put your plants in a sheltered place for a week or two to adjust to the temperature variation in your garden. It 'means much faster growing and longer-lasting flowers' says Monty Don on his popular blog. He also recommends doing the same for young cosmos that are bought in the garden centre too.
Direct planting is a low-maintenance choice that creates a beautiful cottage garden aesthetic. 'I place them in groups so they make drifts and clumps rather than straight lines.' continues Monty.
Simply rake the ground and sprinkle the seeds directly in the bed. You can then thin these out once the seedlings have appeared. However, be sure to wait until all threat of frost is over and ensure that your soil has sufficiently warmed up.
- See: Garden trends 2021 – all the latest looks and new ways to garden
Do cosmos like full sun?
However you start off your plants, cosmos like being planted out in full sun and in moist but well-drained soil. You can also encourage bushier plants by pinching out the tips at 15-20cm, and by staking the plants once they are tall enough.
How to keep your cosmos flowering?
If your cosmos just aren't flowering, you could be making one crucial mistake. In order to keep your cosmos flowering, it is important to deadhead the blooms. This stops the plant putting its energy into creating seeds and instead puts its efforts into creating more flowers.
'What I like to do, is to deadhead really early on as the flower starts to fade and keep them as cut flowers for the house' says Monty Don in this Gardeners' World video. 'If you manage it right, the flowers will keep going week after week'.
'Cut between the main stem and a leaf' advises Sarah Raven in this video from her Perch Hill Gardens 'The lower you go in the plant, the more delay between the flower you've just picked and the next flower.'
Just before the first frost, allow a few blooms to go to seed, so that you can harvest and save the seeds for planting next year.
Do cosmos come back every year?
Cosmos are annuals meaning they do not come back every year. In order to have blooms every year, you will need to resow your seeds the following spring.
The only difference, however, is Chocolate cosmos (also known as cosmos atrosanguineus) which is grown from like a dahlia from a tuber. Chocolate cosmos is loved for its delicious vanillary-chocolate scent and velvety brown flowers, and since it is a perennial, will come back year after year.
Growing cosmos as a cut flower
'Cosmos is one of our absolute favorite plants here' says Sarah Raven in a video from her Perch Hill Gardens. 'They give you the highest productivity of any other cut flower and have a very good vase life'.
To get the most from your floral arrangement, be sure to strip off all leaves and sear the stem ends in boiling water for 10 seconds. You can expect your cosmos to last between six and ten days in a vase.
Blue dining room ideas – 12 beautiful ways to decorate with this soothing color scheme
These blue dining room ideas are perfect for a cool and sophisticated look
By Nicky Morris •
5 ways to design a calm garden retreat, using neutral colors and low-maintenance planting
Restrained materials and a muted color palette are the secrets to this calm garden retreat in the Hollywood Hills
By Rhoda Parry •
How to prune wisteria – and the best time to do it
Learn how to prune wisteria for a healthier plant with maximum blooms
By Melanie Griffiths •
How to prune clematis – everything you need to know for beautiful blooms
Discover how to prune clematis to ensure a beautiful flush of blooms every year
By Holly Reaney •
How to prune azaleas – and when to leave them alone
Find out when and how to prune azaleas to enjoy the best from these colorful flowering shrubs
By Rachel Crow •
How to prune a lemon tree
Learn how to prune a lemon tree to maximize fruit production and keep the plant in good shape
By Melanie Griffiths •
How to prune basil – and the best time to do it
Find out how to prune basil plants the right way for healthy, bushy plants that last longer
By Rachel Crow •
How to prune raspberries
Learn how to prune summer and autumn fruiting raspberries to ensure a bumper crop
By Pippa Blenkinsop •
How to prune lilac
Discover how to prune lilac to keep it look great and flowering every year
By Holly Reaney •
How to prune an apple tree – and when to do it
Keep apple trees in great shape to improve your harvest. Find out how to prune an apple tree with advice from experts
By Karen Darlow •