Growing Cosmos Flowers: How to Plant & Care for Cosmos (2024)

Cosmos are stunning annual flowering plants that will attract butterflies, bees and birds to your garden. It’s easy to grow these plants directly from seed, and they will survive in all types of soil conditions, even if the soil in your area is poor.

Here is everything you need to know about growing and caring for these magical plants!

What are Cosmos Flowers

Cosmos boast brightly coloured, daisy-like flowers that bloom at the ends of slender green stems. The blooms can range from deep mauve to cerise pink, pale pink, orange, red, yellow and white, and span 3 to 5 inches in length. The flowers can be open-cup or bowl-shaped, depending on their age, and the plants themselves can grow up to 6 feet tall.

Cosmos plants bloom prolifically throughout the summer months, which makes them ideal if you need a plant that produces gorgeous cut flowers as well.

How to Grow Cosmos

Where to Plant Cosmos

Cosmos prefers climates that are warm and dry, and these plants are even drought resistant to a degree. They don’t need any particular soil preparations and prefer soil that is not too rich. Planting them in a spot with overly rich or loamy soil will prompt their foliage to grow and reduce the numbers of flowers they produce.

When to Plant Cosmos

If you are planting cosmos from seed, you need to bear in mind that they can take up to 7 weeks to start blooming. It’s advisable to plant your cosmos indoors around 4 to 6 weeks before the last frosts of spring so that they will be blooming once summer arrives. You can plant them in pots or seedling trays containing a quality seed-starting potting soil. You can transplant them into 5-inch pots as soon as they have grown to 3 or 4 inches tall.

How to Plant Cosmos

You can sow your cosmos seeds around one-quarter of an inch deep, and roughly 12-18 inches apart. Remember to plant them after the possibility of frost has passed. You can also plant transplanted plants that you have grown from seed in a sheltered environment like your greenhouse or your home.

How to Care for Cosmos

The best way to prolong the flowering period of your cosmos plants is to deadhead them by removing dead or dying flowers. This boosts the development of new flowers and allows the bushes to form new branches as well.

Some cosmos plants can grow very tall, so it may be necessary to stake them or grow them along a fence. Tying them to stakes or fence posts will protect them from strong winds and other seasonal phenomena. You can also encourage full branching by pinching off the plants’ stem tips and central shoots.

You will need to water your cosmos plants regularly but take care not to over-water them! You may enjoy fewer flowers if you over-water and over-fertilize their soil. Cosmos will easily survive in dry soil, and can also thrive in arid, desert-like conditions.

What is the Meaning of Cosmos Flowers

Along with marigolds, cosmos is one of the birth flowers associated with the month of October. They traditionally symbolize order, harmony, peace, innocence and love. They are also one of the flowers traditionally linked to the 2nd wedding anniversary, and they make for wonderful gifts cut, and ready for planting!

When do cosmos flower?

Cosmos plants flower from mid-spring to late summer.

Does cosmos come back every year?

Yes! These plants are self-seeding, so if you allow the spiky brown seed heads to blow away in the fall, your cosmos plants will self-sow in your garden and spring back next spring.

Do cosmos flowers spread?

Yes, they do. The plant’s self-seeding nature means that you may find plenty of cosmos seedlings popping up in your yard during their growing season. Their beds can become weedy because they self-seed too, so be sure to check them often.

How tall do cosmos flowers get?

Cosmos flowers can grow anywhere up to 6 feet tall! If you want shorter, bushier plants, cut off the flowers and new shoots at the tips to encourage even branching.

Should I deadhead cosmos?

Absolutely. Deadheading your cosmos will ensure that it flowers prolifically throughout its blooming season.

Does cosmos reseed itself?

Yes, it does. You can also store the seeds for the next spring and summer growing season by gathering your cosmos plants’ seed heads, removing the seeds from them, and storing them somewhere cool, dark and dry.

Should I grow cosmos seeds or plants?

That depends on your personal preference. Cosmos is easy to grow from seed, but it can take weeks to start flowering. If you want to see white and pink flowers adorning your garden as soon as possible, invest in some ready-grown cosmos plants instead.

What insects & diseases affect cosmos flowers?

There are three kinds of pests that most often affect cosmos: thrips, aphids, and lygus plant bugs. It is not advisable to treat these pests with insecticides, as poisons can damage your garden’s ecosystem and harm the nature around it.

Instead, try planting marigolds and chrysanthemums with your cosmos plants. These flowering plants produce stunning blooms of their own, and also help to repel pests. Additionally, you can also try using neem oil as a foliar spray to get rid of these insects.

Do bees & butterflies like cosmos?

Very much! Planting cosmos can attract all kinds of pollinators to your garden, including bees, butterflies and even seed-eating birds.

Is cosmos poisonous to dogs?

Cosmos is non-toxic to dogs, cats and even children, making it a safe plant to grow in a family garden.

Can cosmos grow in pots?

Yes! You can grow cosmos in a heavy pot that is at least 12 inches in diameter and has sufficient drainage holes at the bottom. Remember to fill the bottom of your container with gravel before adding your soil to improve its drainage capacity.

Why do my cosmos plants have no flowers?

There are a number of reasons your cosmos plants may not be blooming. They may not be old enough to flower yet, or you may be over-fertilizing them with a nitrogen-based fertilizer. You should preferably only fertilize your cosmos on planting using a 5-10-10 formula.

The weather may also be too cold or wet for their liking. If your cosmos seeds are over a year old, this could also contribute to poor growth and bloom development.

Lily Thornton

Lily’s love for flowers and plants was nurtured in her grandmother’s vibrant garden. Over the years, this affection blossomed into a full-fledged passion for horticulture.

With formal training in botany and countless hours in her own backyard oasis, Lily has cultivated a deep understanding of plant care and garden design.