A garden favorite for summer colours, learn how to grow cosmos and you can enjoy clouds of these daisy-like flowers dancing in the breeze and filling garden beds and borders.
From pale pastels and white to bubblegum pink, crimson, orange, and other zingy hues, these annuals are a perennial favorite for flower bed ideas. They will delight themselves for several years, filling your yards with their open blooms that can last for months and months, adding to your color palette of late summer blooms and still displaying their showy blooms until the first frost of fall.
Cosmos comes from the Greek word ‘kosmos’, which means beautiful, growing tall with fluffy falling foliage, and cosmos is definitely one to include if you’re planning a cut flower garden where the more flowers you choose, the more flowers you’ll get.
There are many cultivars available, including doubles, others with tubular rays and some bicolours, in long and compact varieties.
Once you know how to grow cosmos, you will use it to brighten all corners of your garden.
How does the universe grow from the seed?
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It’s easy to learn how to grow cosmos from seed and can be sown at any time throughout the spring depending on what hardiness zone you live in. The seeds are large, long and fluffy, so they are easy to handle and germinate quickly.
“Cosmos are the best-blooming, low-maintenance plants in the world. With a little bit of effort, they give you buckets of fresh cut flowers and they have good vase life, too,” says Sarah Raven, a plant expert. (Opens in a new tab).
These pollen-rich flowers are also an excellent lure for bees and other pollinators to attract them to your wildlife garden. Sarah agrees, “It’s stacked with nectar and pollen, so bees and butterflies love it.” also.
Cosmos Pepinatusmost common, also known as Mexican aster, originates from the Americas.
When it comes to growing cosmos from seed, you have two options. You can grow them in units or seed trays indoors, or sow them directly in the garden. There are benefits to both.
(Image credit: Future/Leigh Clapp)
How to successfully develop the universe?
Growing cosmos in seed units or trays indoors to start them off gives you more control over flowering. Keeping them off the ground and under cover will also protect the tender seedlings from slugs and harsh weather. Plus, since you’re starting your plants indoors, you can start planting earlier — in early spring — so you’ll have established blooms that attract bees by early summer.
Sow indoors in unit or seed trays, covered with about 2mm of good, fresh compost. Water from below, allow excess water to drain away and place in a warm location, ideally 60 to 70 degrees Fahrenheit (16 to 21 degrees Celsius), to germinate, which takes about 30 days.
Move the seedlings to a cool or light sheltered location for a few weeks before transplanting outside to harden them off. This will result in “faster-growing, longer-lasting flowers,” says horticulturist Monty Don on his blog. (Opens in a new tab). He also recommends doing the same for young cosmos purchased at the garden center as well.
Direct sowing outdoors
(Image credit: Lee Clapp)
If you choose to direct the cosmos outdoors, this is a low-maintenance option and is nice for a home garden idea. “I put them in groups so they make drifts and clumps rather than straight lines,” Monty says.
To learn how to grow cosmos seeds outdoors, wait for the soil to warm up, then:
- Rake your seed area to remove any clumps of soil and achieve a crumbly texture;
- Cosmos doesn’t need any special soil preparation – in fact, soil that’s too rich will encourage foliage rather than flowers;
- Sow the seeds gently, about 2-3 inches (5-8 cm) apart;
- Thinning seedlings
- Water until firm but do not over water as this can result in fewer flowers.
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Where does cosmos grow best?
Cosmea grows best in a sunny spot, sheltered from the wind, with light, well-drained soil. Mulching is recommended to conserve moisture, and if you learn how to make leaf mulch, you can use your own organic garden materials.
If you live in a very warm area that can suffer from extreme heat, cosmos will tolerate part shade.
Cosmos tolerates most pH levels, but does best in neutral to alkaline soil and is quite drought tolerant, so it can be a useful addition to your planting palette if you’re planning a dry garden. Long or wet and cool periods are detrimental and can delay flowering.
Plant your world in a collection to make a true focal statement for late summer through fall and into the first frost. This will also attract more bees than if it were spread out in the garden.
Cosmos is good for cheery color in any area of the backyard and goes well with a range of styles—from planting a cottage garden border, creating a prairie-style landscape planting design, or planting a wildflower meadow.
Sarah Raven says, “I love to grow lots of different types of cosmos, to combine different heights and colors in pots and to create gorgeous layers of intense color.”
They are also excellent for companion planting alongside vegetable and fruit crops in the kitchen garden, as they entice pest predators and valuable pollinators. ‘We plant the cosmos with our vegetables, in rows to help support one another,’ explain Henrietta Courtauld and Bridget Elworthy, The Land Gardeners. (Opens in a new tab).
When to plant the seeds of the universe
(Image credit: Lee Clapp)
Early spring is the best time to sow cosmea seeds under cover indoors, which will then produce flowers that bloom early in the summer.
Alternatively, you can direct the cosmos seeds into their flowering position once the soil has warmed. This will vary depending on the area you live in, but it will be from around late May in cooler areas, and earlier in warmer areas.
Purchased seedlings can be planted in late May or June.
Is the universe easy to grow?
Yes, cosmos is easy to grow. “Cosmos is one of the easiest flowers to grow from seed sown directly into the garden bed,” advises the experts at American Meadows. (Opens in a new tab).
“As it grows, water the cosmos if necessary, and water it regularly,” says Sarah Raven.
Cosmos has few pest problems. Watch out for slugs and snails, especially when the plants are young and tender, so use slug barriers. To avoid powdery mildew and fungal diseases, make sure the plants have room and that the soil is not soggy. Cosmos prefers dry, arid soil to moist conditions. Soil that is too wet may lead to disease,” advises American Lawn Experts.
(Image credit: sarahraven.com/Jonathan Buckley)
Can you put the universe in pots?
Cosmos, especially the shorter varieties, can be grown in pots, and make attractive patio and container plants. Since they are so good at attracting beneficial insects to your vegetable and fruit crops, why not include them in your vegetable garden container ideas?
Try a mix of shorter dwarf cosmic varieties, such as Sensation and Sonata mix, grown from seed, or buy them as cuttings and plant from May, about 11 inches (30 cm) apart. Cosmos does particularly well in pots containing zinnias.
Use a light potting mix, in pots with good drainage and place in a sunny location. Water regularly and feed it with a liquid fertilizer every few weeks during the summer.
(Image credit: Lee Clapp)
How do you keep the universe thriving?
If your world is not prosperous, you may be making a huge mistake. An important step in how to grow cosmos and keep it blooming is to remove blooms. This prevents the plant from putting its energy into making seeds and instead puts its efforts into producing more flowers.
You’re probably busy in the garden with roses, dead petunias, and other flowers, so add cosmos to the list.
As long as you don’t cut the plants directly to the ground, but over a pair of leaves, more buds will form to fill your vases next week and more the week after that. The lower the plant, Sarah Raven explains, the greater the delay between the flower you just picked and the next flower.
“We love cosmos because it’s light and airy and has the joy of endless giving—every time another dead flower appears,” Land Gardeners add.
(Image credit: Thompson & Morgan)
Does the universe come back every year?
Almost all cosmos are annals, which means they don’t come back every year. For it to bloom every year, you will need to resow the seeds the following spring.
The only exception to this rule is the world of chocolate, universe atrosanguineus, Which grows like a dahlia from a tuber and is a perennial. Chocolate Cosmos is loved for its delicious vanilla scent and velvety brown flowers, and because it’s a perennial, it will come back year after year.
An annual cosmos can also be a self-seed. If you let some of your cosmos flowers die naturally and fall to the ground the seeds will germinate on their own. Allowing plants to self-seed is a step on the path to creating an eco-friendly garden.
You may also want to try collecting seeds to save them from the flowers to plant next spring. If you want to save seeds, know that hybrids will not grow properly, so choose varieties that are openly pollinated, as opposed to hybrids—which can vary greatly in the next generation.
You can collect cosmos seeds at the same time you collect zinnia seeds and other flower seeds you like. This is a cost effective way to fill your garden with flowers, year after year.
Spread the collected seeds in your garden or store them in envelopes or paper bags intended for next year’s sowing.
(Image credit: Lee Clapp)
Do you hack the universe?
You should read growing tips for cosmos to encourage branching and flowering, and in about 12 weeks you will see your first flowers.
If you then want to enjoy these flowers at home as well as in the garden, cosmea makes excellent cut flowers. To harvest cut flowers, cut the cosmea flowers when they begin to emerge in the morning, when there will be the most moisture making them less likely to wilt.
Submerge the flowers in a bucket of warm water, stripping off the bottom leaves to avoid them in the water. There are many tricks on how to keep flowers fresh in a vase. Recut the stems regularly, refresh the water, and the cosmos should last up to 10 days in the vase.
(Image credit: Pippa Blenkinsop)
Does the universe need a mask?
The taller types of cosmos will need to be petted to keep them from unraveling.
It can grow up to 8 feet (2.5 m) tall and the flowers can be up to 3 inches (8 cm) across.
`It is worth taking the time to capitalize on them properly as they benefit greatly from early direct growth. ‘If it collapses, it will never grow or flower as well as when supported vertically,’ Sarah Raven explains.
How often should I water the cosmos?
Water the cosmos regularly until it is established, or during periods of drought. However, it is important not to overwater the cosmos as this can result in plants with fewer flowers.
Cosmos can tolerate dry soil, even in hot, sunny areas. In fact, they prefer poor soil and seem to thrive on a little neglect!
(Image credit: Lee Clapp)
Is the universe like the sun or the shadow?
Cosmos are sun-loving flowers, though they will tolerate a little shade in warmer climates.
Cosmos and zinnias make good companions and also mix them with other sun-loving plants in borders, beds, lawn plantings, and containers, such as Verbena bonarensis Alstroemeria, calendula, eryngium, dahlias and nepeta.
‘Cosmos’ can be combined with almost all full-sun border plants to give that mid-to-late season “wow” factor. Garden designer Charlie Bloom says:
The range of colors allows for a variety of combinations, whether it’s bright and breezy or more subtle, so there’s plenty of scope.
