Cosmos are popular cottage garden features, with daisy-like blooms. Some even have familiar delicious fragrances. Find out everything you need to know to grow cosmos in your garden.
Plant Biography
BOTANICAL NAME
Cosmos
COMMON NAME
Cosmos
NATIVE TO
Cosmos plants are native to North and South America, including countries like Mexico, Costa Rica, Colombia, Argentina, and several states of the USA.
DESCRIPTION
These flowers are often described as being ‘saucer-like’ in shape, cupped upwards. Some have distinctly separated petals, other cosmos have fused or semi-fused petals.
What type of plant is it?
There are annual varieties, and a perennial variety, Cosmos atrosanguineus. You can also choose biennial varieties, which take a little longer to flower.
What colours do Cosmos come in?
You can most commonly get cosmos in pink, red, white, orange or yellow. However, Cosmos atrosanguineus has very dark red blooms and smells like chocolate.
When do these plants flower?
Cosmos can flower from May through to October depending on the variety and conditions.
Where to grow Cosmos
These plants are sun-lovers. Therefore, choose a warm, bright spot in the garden with free-draining soil.
Where not to grow Cosmos
Either poor and dry soils or very heavy and wet soils won’t suit cosmos plants. These plants should also avoid spots with a lot of shade.
Is this plant drought-tolerant?
Once they have been established, yes, cosmos plants can be drought tolerant.
How to grow Cosmos successfully
Firstly, sure you give it the right growing conditions, and make sure the area is clear of weeds. Try not to sow them earlier than March or later than April, and they should be pretty easy to grow beyond this.
Do they require supports?
Some taller cosmos varieties do benefit from staking. You could choose from a couple of methods to do this, perhaps depending on how many flowers could benefit from some support.
The first method involves using bamboo canes as a stake. You could loosely tie the stems of your cosmos plants to the bamboo using twine or string, just to keep the plant upright.
Finally, the other method involves using pea netting. You can simply spread this across your cosmos border, supported by bamboo canes at the corners. As your cosmos grow, they can grow through the netting, which will give them light support. The netting will initially be quite visible, but as the foliage develops, it should be well-covered.
Is it good for pollinators?
Yes, cosmos are great for pollinators. Plus, bees in particular are quite fond of them, having nice open blooms which make access to nectar effortless.
Is it good for wildlife?
Not only are cosmos good for pollinators, but they also encourage other beneficial insects into the garden. Also, their seeds can be beneficial to birds too.
How to choose the right variety for your garden
Your choice may be determined by how long you want your cosmos display to last, and how much time you can commit to growing them.
First, hardy annual varieties are the easiest to grow and are reliably sown straight into borders. Or you could choose half-hardy or tender annuals, but these require a little more time, as they should be sown indoors. Alternatively, you could grow bedding varieties, which are generally treated as annuals. Simply remove them once their display has finished in the early autumn.
Also, you could consider biennial varieties. You can grow these easily from seed. However, you will need a little patience for flowers. Can be sown outdoors or indoors depending on how hardy the variety is. Then, the flowers will typically appear the second year after sowing.
How big will it get
This depends on the variety you choose. Some varieties grow over one metre in height (three feet), whilst others are more compact. These smaller varieties shouldn’t grow larger than 60cm (two feet).
How to plant Cosmos
Cosmos plants are often grown from seed. Hardy varieties can be sown straight into the garden or your preferred container. More tender varieties can be sown indoors, to be planted out once the risk of frost has passed.
All you need is to find the right position, with well-draining soil, and your cosmos should be quite happy.
How to care for Cosmos
These plants are quite low maintenance, but there are a couple of ways you can help them look their best.
Once your seedling has approximately 2-3 leaf pairs, by pinching out the growing tups, your plants will be bushier, and more productive with blooms.
Staking can benefit taller varieties, and chocolate cosmos (Cosmos atrosanguineus) being perennial benefits from winter protection. It is best to grow this variety in containers or move them into containers after flowering, so they can be overwintered indoors.
Water young plants regularly until they are established, then water less frequently. If there are some hot and dry periods, keep an eye on them, as they may need more regular watering. However, if your cosmos are growing in containers, water them regularly, as they will dry out quickly.
Do they spread?
Cosmos plants can spread by self-seeding but are more likely to succeed if you collect the seeds and sow them yourself.
How to keep it looking good
One of the best ways to make your cosmos display look fantastic is deadheading spent blooms. This will save the energy the plant puts into seed production for more flower production.
Does Cosmos need deadheading?
Cosmos does not need to be deadheaded, but it can help to extend and improve your flowering display.
Does it need pruning, and when should they be pruned?
No, cosmos plants do not need pruning.
How to propagate these plants
This can depend on the type of cosmos you have. Most varieties (annuals and biennials) are best propagated by seed, so collect them up once your flowers have faded. These seeds can then be sown indoors or in the garden next year.
If you have the perennial chocolate cosmos (Cosmos atrosanguineus), lifting and dividing is the best way to propagate. Simply lift the tubers from the ground, and separate them to replant as individual plants.
What problems can Cosmos have?
Generally, cosmos tend to be trouble-free. Just keep an eye out for slug and snail damage on young seedlings.
Varieties of Cosmos to have
For a fantastically fragrant perennial variety, Cosmos atrosanguineus chocolate cosmos is a popular choice. It earns its common name from its distinctive chocolate and vanilla scent and has moody, dark red blooms.
A great set of cosmos varieties to look out for is the Apollo series, each having similar shapes but different colours. This is great if you want to add some consistently shaped flowers, whilst having the depth of a variety of colours. Cosmos bipinnatus ‘Apollo White’ has pure white blooms with a bright yellow centre. Cosmos bipinnatus ‘Apollo pink’ is a light and soft pink shade, and Cosmos bipinnatus ‘Apollo Carmine’ in a brighter, fuchsia shade.
Alternatively, a lovely annual variety with fluted petals, consider Cosmos bipinnatus ‘Sea Shells’. The curled petals earned this variety its name, which adds a dainty, soft look to garden borders and containers.
Best time of year to buy this plant
Seeds for this plant can be purchased throughout the year. Alternatively, garden-ready plants can be found in garden centres from mid-May.
The best garden design style for this plant
Cosmos are ideal for cottage gardens but also work well in containers, and wildlife gardens, and are grown for cut flowers.
Find out how to grow Jasmine:
Or check out my Pinterest board for more ideas:
David Domoney is a Chartered Horticulturalist, Broadcaster, and Author. David has worked with a number of the UK’s leading garden retailers as a plant buyer and strategic consultant. With more than 30 years experience, in horticulture, David is as passionate about plants now as he was when he bought his first plant at a village fete.
Leave A Comment