Cosmos is a genus, with the same common name of cosmos, consisting of flowering plants in the sunflower family. They are native to Mexico, where they bloom in swathes of pink, white, and orange in sun-baked meadows and scrub. The name derives from the Greek kosmos, meaning ‘beauty and harmony of the universe’, and was adopted by Spanish missionary priests in Mexico, who appreciated the flower’s evenly arranged circle of petals.
Cosmos are herbaceous perennial plants or annual plants. The leaves are simple, pinnate, or bipinnate, and arranged in opposite pairs. The flowers are produced in a capitulum with a ring of broad ray florets and a center of disc florets; flower color is very variable between the different species. The genus includes several ornamental plants popular in gardens. Numerous hybrids and cultivars have been selected and named. Cosmos grow in both beds and containers—and they also make great cut flowers.
Table of Contents
1 - 6 feet
1 - 3 feet
6.0 - 6.8
Types of Cosmos
There are over 25 species of cosmos. However, three species are most commonly used in gardens and landscaping. Cosmos sulphureus is native to Mexico, Central America, and northern South America. With golden yellow blooms, it is very drought tolerant and loves hot weather. The plant grows 2 to 6 feet tall and comes in double and semi-double flowers. Some of the more recent cultivars tend to be shorter, more orangy, and with smaller flowers.
Cosmos bipinnatus are colorful daisy-like flowers that come in white, pinks, reds, and orange. At 1 to 4 feet in height, they are shorter than C. suphureus and are available in several popular hybrid series. Although they are not quite as heat tolerant as C. sulphureus, C. bipinnatus will grow well in just about any sunny space.
Chocolate cosmos are a separate species: Cosmos atrosanguineus. The dark red flowers smell like chocolate. This perennial is hardy but it is higher maintenance than annual cosmos. Like dahlias, it grows from tubers.
Other common cosmos cultivars include:
With its cool pastel coloring, ‘Apricot Lemonade’ is as refreshing as a cold drink in the heat of summer. This C. bipinnatus cultivar has delicate flowers that open with apricot-colored petals and a lilac blush, then gradually fade to a buttery yellow with a pink blush. Single flowers measure three to four inches across and show a lovely lavender hue on the bottom sides of their petals. ‘Apricot Lemonade’ plants are compact, reaching two to two and half feet tall. They have sturdy stems, making them an excellent addition to your cut flower garden.
‘Bright Lights’ is a mix of C. sulphureus blooms that come in shades of yellow, gold, orange, and scarlet. Semi-double blossoms measure two and a half inches across, covering plants that grow to be up to three feet tall.
Sometimes flowers look as sweet as candy, and ‘Candystripe’ is no exception, with its charming bicolored petals. This cultivar of C. bipinnatus has white petals with crimson margins and faint reddish pink stripes. Three- to four-inch single flowers sit atop plants that reach three to six feet tall.
‘Choca Mocha’ is a cultivar of C. atrosanguineus, the species that is also known as “chocolate cosmos,” not only for its coloring, but also for its smell. ‘Choca Mocha’ blooms have deep brownish-red petals and dark centers, measure one and a half inches across, and have a chocolatey fragrance. Single blooms grow on petite plants that reach 10 to 12 inches tall. Like other varieties of C. atrosanguineus, ‘Choca Mocha’ is usually propagated from live plants or tubers rather than seeds.
As the name indicates, Cosmos Cosmic Orange features bright orange-colored flowers that are extremely attractive and eye-catching. The plant is heat, humidity, and drought tolerant which makes it easy to grow and maintain all summer long.
Cosmos Cosmic Red has double flowers that are a striking scarlet red. The flowers are very vibrant and attractive and that is the reason why the Cosmic Red variety is so popular in gardens. They produce flowers from summer till fall, making your garden a sight to see and remember!
Featuring vibrant yellow-golden flowers, Cosmos Cosmic Yellow is yet another brightly colored, super attractive type of Cosmos sulphureus that is popular for all the right reasons. Being easy to grow and maintain, and their great performance as cut flowers, Cosmic Yellow are not just great garden plants but are a great ornamental variety as well.
‘Cupcake White’ is a Mexican aster that has delicate four- to five-inch blooms that look very much like cupcake wrappers – its petals are fused into a lovely chalice shape. Some flowers have additional tufted petals in the centers. These open-pollinated plants are bushy and will grow to be 24 to 36 inches in height.
Cupcakes and Saucers
A variation on the ‘Cupcake’ variety mentioned above, ‘Cupcakes and Saucers’ is truly out of the ordinary – its outer petals are fused into a chalice shape, but flowers contain frilly petals within the chalice as well. Four-foot plants are bedecked with double and semi-double flowers in shades of white, pink, and lavender, with yellow centers.
‘Daydream’ features petals that are dark pink around yellow centers, gently fading to a paler pink towards the tips. Plants grow to be five to six feet tall and are covered with three-inch flowers.
‘Diablo’ is an heirloom variety of sulfur cosmos in a fiery, reddish orange hue that will certainly bring the heat. Taller than ‘Bright Lights’ mentioned above, ‘Diablo’ grows to be four to five feet tall and holds its two-inch flowers on wiry stems. Despite its devilish name, ‘Diablo’ has quite the pedigree, and was named an All-America Selections winner in 1974.
Double Click Bicolor Violet
‘Double Click Bicolor Violet’ is a C. bipinnatus variety that you’d be forgiven for mistaking for a carnation. In luscious shades of violet, lavender, white, and cream, these semi-double and double flowers are a riot of ruffles. Open pollinated plants reach 42 to 46 inches tall, and showcase flowers that are two to three inches wide. Flowers bloom in 75 to 90 days after sowing.
Double Click Cranberries
‘Double Click Cranberries’ is a C. bipinnatus variety that comes in a rich burgundy color with double and semi-double blooms. Flowers are two to three inches wide and held aloft on sturdy stems, making this type perfect to use in flower arrangements. ‘Double Click Cranberries’ plants grow to be 42 to 46 inches tall, with flowers blooming 60 to 90 days after sowing.
‘Double Take’ flowers are ivory colored with magenta margins, and blooms are semi-double and double, with frilly petals around yellow centers. The flowers of this C. bipinnatus cultivar are four inches wide, and are held on three- to four-foot plants.
Cosmos Picotee adds beauty and grace to any garden with its beautiful flowers. The flowers are white-mauve in color with edges a dark purple-carmine. The fern-like foliage is dark green that makes the flowers stand out even more stunningly. They are excellent cut flowers that can last for about 7 to 10 days in a vase, making them great ornamental variety as well.
Psyche, a figure from Greek Mythology, gives her name to this cultivar. Poor Psyche was so lovely she unwittingly provoked the jealousy – and wrath – of the goddess Aphrodite. This captivating white C. bipinnatus cultivar has three- to four-inch double blooms with frilly outer petals and flouncy inner petals around bright yellow centers. ‘Psyche White’ grows to be two to four feet in height, flowering in eight to 12 weeks after sowing.
‘Purity,’ a variety of C. bipinnatus, has single, white blooms that reach four to six inches in width. Plants grow to be three to four feet tall, and provide a mass of white flowers in 75 to 90 days after sowing.
An open-pollinated heirloom variety of C. bipinnatus, ‘Radiance’ has single flowers that are a deep magenta around yellow centers, radiating out to a rosy pink along its petals. Plants reach three to five feet in height and are covered profusely in three- to four-inch flowers, starting 60 to 90 days after sowing.
Rose Bon Bon
This rose-colored cultivar of C. bipinnatus has all the subtlety of a multi-layered, ruffled, pink prom dress – that is to say, none at all. Yet it is charming nonetheless, with its curled petals and double blooms, looking much like a carnation. Three-inch flowers grow on plants that reach three to four feet tall. ‘Rose Bon Bon’ has long stems, making these exquisite rose-hued blooms perfect for vases. And they’ll be ready to cut in 60 to 90 days after sowing.
‘Rosetta,’ a bicolor C. bipinnatus cultivar, has delicately striped petals in white and blushing shades of pink. Plants reach 25 to 32 inches tall and are loaded with large, four-inch, single and semi-double flowers.
‘Rubenza’ is a C. bipinnatus cultivar that brings to mind the deep red accent color in works by the Flemish painter, Rubens. Single, three-inch blooms start out a shade of ruby red and as time passes, they fade to a lovely shade of antique rose. Open pollinated plants reach 24 to 32 inches tall and are early to bloom, opening their first buds in 75 to 90 days.
A truly exceptional heirloom C. bipinnatus variety, ‘Sea Shells’ has tubular petals. ‘Sea Shells’ is a mix, with flowers in shades of white, pink, rose, and crimson. Blooms are two and a half to three inches across on plants that grow to be three to five feet tall. ‘Sea Shells’ may take a bit longer to reach maturity compared to some of our other selections – allow 90 to 110 days from sowing for the first buds to burst.
The open-pollinated ‘Sensation’ mix features single flowers in gorgeous shades of white, pink, rose, and crimson. Requiring 75 to 90 days from seed to flower, these plants can grow to be quite large, between three to six feet in height, and are topped with lovely three- to four-inch blooms. ‘Sensation,’ a cultivar of C. bipinnatus, was the All-America Selections Winner in the flower category in 1936.
‘Sonata’ is an open-pollinated C. bipinnatus variety that won the Fleuroselect Novelty Award in 1991. Single flowers with wide petals come in shades of white, rose, pink, and cherry. These compact plants grow to be 20 to 24 inches tall and are covered with flowers that are two and a half to three inches wide.
‘Velouette’ offers an assortment of single, velvety flowers – some are white with deep red stripes, others are dark red with faint white striping, and still others have petals whose stripey patterns lie somewhere in between. Yellow centers stand out among these striking petals. An early flowering C. bipinnatus cultivar, ‘Velouette’ will show its first color in as little as 70 days. Plants grow to be 25 to 32 inches tall and are covered with large flowers.
Versailles Tetra Red
In a shade as deep as a fine French wine, ‘Versailles Tetra Red’ will conjure up the regality of the famous Parisian chateau it takes its name from. Single, burgundy-colored flowers measure two and a half inches across on plants that can grow up to four feet tall. An open pollinated C. bipinnatus cultivar, ‘Versailles Tetra Red’ will begin to bloom 60 to 90 days after sowing. This variety makes an excellent cut flower for use in arrangements.
‘White Knight’ is a C. bipinnatus cultivar in the Double Click series with ruffled, semi-double to double creamy white flowers that measure two and a half to three inches across. Plants grow to be three feet in height and produce flowers in 60 to 90 days. For a stunning display of all white blooms, try combining ‘White Knight’ with our other white selections, ‘Purity,’ ‘Psyche White,’ and ‘Cupcakes’
‘Xanthos’ is a C. bipinnatus cultivar with lovely, pale yellow flowers that are on the small side, at two to two and a half inches across. A dwarf variety, ‘Xanthos’ won a prestigious Fleuroselect Gold Medal Award in 2016 for its “beauty, innovation, use, and garden performance.” It grows to two feet tall and makes a great choice for container gardening. And making it even more attractive, it flowers in just 70 days after sowing.
The bicolored petals of ‘Xsenia’ might be described as terra cotta with rose colored margins – but these flowers seem to change color depending on the time of day. In 75 to 90 days after sowing seeds, ‘Xsenia’ will produce two and a half- to three-inch blooms on plants that grow to be 24 to 28 inches tall. ‘Xsenia’ won a Fleuroselect Novelty Award in 2018.
When to Plant Cosmos
Direct-sow seeds outdoors once the danger of frost has passed.
Alternatively, sow seeds indoors 4 to 6 weeks before your last spring frost date in trays or pots with a good seed-starting mixture. Move them into 5-inch pots as soon as they’re 3 or 4 inches tall.
Young plants (transplants) can be planted outdoors once the danger of frost has passed.
Choosing and Preparing a Planting Site
Cosmos don’t need any special soil preparation. In fact, they like soil that is not too rich, as rich soil will encourage foliage at the expense of blooms.
Soil should be well-draining.
Cosmos are tolerant of most soil pH levels, but grow best in neutral to alkaline soils.
Cosmos can tolerate warm, dry weather very well. They are even drought-tolerant.
Depending on the variety, cosmos can grow anywhere between 18 to 60 inches tall, so plan accordingly.
How to Plant Cosmos
Just sow seeds lightly—no more than 1/4-inch deep.
Thin to 12–18 inches apart when seedlings are a few inches tall.
If you are growing cosmos from seeds, be mindful that it takes about 7 weeks to first bloom. After that, though, your flowers should continue to bloom until the first fall frost.
If you let the spiky-brown seed heads blow away during the fall, cosmos are likely to self-sow throughout your garden.
How to Get Cosmos to Bloom
Cosmos plants need full sun to bloom. Even the hint of shade, can restrict flowering. Also, to encourage more blooms, you need to deadhead the old blooms. For faster blooms, prune between the main stem and a leaf. The lower you cut in the stem, the longer it takes to grow more flowers.
Cosmos grow easily in beds and make great cut flowers. When established, the plants can handle drought, poor soil conditions, and general neglect. They even self-sow. This is a truly low-maintenance plant.
While some pests, like aphids, flea beetles, and thrips feed on cosmos, they're easy to control with a strong spray of water or insecticidal soap. Aster yellows, bacterial wilt, and powdery mildew may also affect cosmos. Space plants accordingly to ensure good airflow to avoid diseases.
Taller varieties look good in the middle or rear of the border with goat's beard, coneflowers, and black-eyed Susans. Shorter varieties make very colorful, airy edging plants.
For the best flowering, choose a site that gets full sun. Cosmos will grow in partial shade but will have fewer blooms and be less vigorous when planted in shady areas. These plants will also thrive under uninterrupted full sun in the hottest conditions, much like their native habitat: the arid regions of Mexico and Central America.
Cosmos plants prefer a neutral soil with a pH of 6.0 to 8.0, although they will grow in poor soil where many flowering plants languish. They perform best in medium moisture, well-drained soils, but they will perform adequately in dry soils. Avoid planting in a rich soil; it can cause the plants to get too tall and flop over. You can prevent drooping by staking the plants or growing them close to other plants that can support them.
Once established, you will not need to water your cosmos plants unless there is a prolonged drought. Where water is limited, these are the last plants that require irrigation.
Temperature and Humidity
Hot weather is ideal for cosmos, and they thrive in any humidity level.
Fertilizing can negatively impact cosmos. Cosmos can handle poor soil. Too much fertilizer can often lead to strong plants with lots of foliage but few blooms. Unless your plants seem to be struggling, these plants do not need fertilizer.
Harvesting Seeds and Cut Flowers
To harvest more seeds, remember to leave a few flowers on the plant because they will self-seed.
You can cut the flowers off anytime after blooming, but it’s best to pick some right when the petals have opened.
If you cut the blossoms when they first open, they’ll last more than a week in water. Simply strip off the lower leaves and put them in a vase.
Pruning and Propagating Cosmos
The only real maintenance cosmos plants need is deadheading which will prolong the flowering season. If you fall behind, shear the plants by about one-third, when most flowers have faded. This kind of pruning produces a second flush of leaves and flowers. By the end of the season, you can cut off the plants at ground level or pull them up, roots and all. However, if you leave the plants in place, they may self-seed for the following growing season.
Cosmos plants readily self-seed. It's best to propagate these plants after the threat of frost is gone. Although sowing seeds is the best and easiest way to propagate this plant, you can also propagate via stem cutting. When you take stem trimmings, it stimulates more leaf and flower growth. Besides seed, stem cutting is the best way to propagate this plant. Here's how you do it:
You'll need sterile pruning shears or scissors and a pot of sterile, well-draining potting soil.
Fill a small 3-inch container with moistened potting soil. Using a pencil tip, push straight down in the soil about 1 to 2 inches deep, making a shallow hole.
Look for a cosmos shoot that has 3 to 5 leaf nodes on the stem. Cut under the last leaf node. At the last leaf node, carefully cut off the leaves, leaving the node intact for new growth.
Bury the cut tip of the stem in the pencil-made hole. Make sure that the last leaf node is above the soil line. Push down the soil around the stem, compacting the soil to keep the stem upright and in place.
Water generously and keep moist. You should notice new leaf growth within three weeks. If you do, you can gently pull the root ball out of the container, Transplant the root ball to its new location.
Potting and Repotting Cosmos
When growing cosmos in pots, make sure the container has bottom drainage holes. Cosmos can't handle overly wet, soggy soil. Plan on growing one cosmos plant per gallon of your container. If growing in pots, do not enrich the soil, it makes the plants grow tall, leggy, and droopy. Also, tall varieties will need staking in containers. At the very least, plan on using at least a heavy, 12-inch diameter container.
Cosmos is an annual. If left outside in frosty temperatures, they will die. However, at the end of the growing season, if you allow the dead flower heads to drop their seeds, cosmos seeds will go dormant and sprout when the soil warms up again in the spring.
If you have a potted cosmos in a container and want to keep your cosmos alive over the winter season, you will need a bright full sun growing lamp for at least 7 hours a day. You will need to snip off any blooms as they form. This plant's life cycle ends with flowering when it drops its seeds for the next growing season.
Common Problems With Cosmos
Cosmos are easy to grow and maintain over the growing season. They are usually resistant to disease, and most insects; however, some pests can become a nuisance and affect their growth.
Wilting or Leaf Discoloration
If your plant has ample water and is not wilting from a lack of hydration, there are two possible causes.
A plant that is wilting with leaf discoloration might have a common fusarium fungal infection. If you dig up the plant and notice a pink mass on the roots, then the plant likely has fusarium. The whole plant is beyond help, will die, and should be disposed of to stop the fungus spread.
If you dig up the roots and they look healthy, the plant may have a bacterial wilt infection. The bacteria cause the stems to wilt at their base. This plant will die and should be disposed of.
Yellowing Leaves and Leaf Drop
Powdery mildew mainly affects plants in the shade. Fungus spores fly through the air and attach to a host plant in a shady spot. It creates a powdery white coating on leaves and causes leaves to yellow and fall off. To prevent powdery mildew, provide your plants good circulation, bright light, and avoid getting water on the leaves. If your plant has fungus, use a horticultural fungicide according to the package instructions.
Flowers Distorting or Stunting in Growth
As a member of the aster family, cosmos can get aster yellows, a disease spread by leafhoppers (a tiny grasshopper-looking insect). The leaves will get yellow mottling on the leaves, and the flowers will appear distorted or stunted. Dispose of these plants since there is nothing you can do help them recover.
Benefits of Cosmos
They attract bees, butterflies and other beneficial insects
Their open flowers provide easy access to nectar and pollen. You can never have enough pollinators and predator insects in your garden, helping pollinate and pest manage for you. Cosmos flowers are magnets for beneficial insects like lacewings, parasitic wasps, tachinid flies and hoverflies that feed on many pest insects and provide free pollination services.
They are easy to grow
Even in tough, hot or dry conditions with little water. They seem to flower best in poor soils with less organic matter which encourages lots of leaves at the expense of blooms. They are often seen growing along the road side in full sun, with no fertilizer in the soil and surviving on rain and dew. Perfect if you have a difficult climate!
These pretty flowers will self-sow
If you just allow your plants to die naturally, the dead flowers will fall to the soil. When the conditions are right, cosmos seeds will germinate all by themselves, saving you time seed raising.
Long flowering and fabulous feature plants
Cosmos blooms can last many months, so they’re great value. When planted in a group, they are an attractive focal point and will attract more bees than just dotted around your garden as single plants. These clever insects know they use less energy flying from flower to flower for a free feed, when they’re all in one spot.
If you grow from organic seeds and don’t use chemicals, the pretty petals of Cosmos sulphureus (C. bipinnatus, C. caudatus or Mexican Aster) are also edible and brighten up salads.
Pests don’t seem to bother them
A low-maintenance flower without many pest problems is a bonus. Ideally, sow your cosmos in amongst other flowers like marigolds and nasturtiums, vegetables and flowering herbs. A diversely planted garden, even in a pot or tub will reduce the likelihood of an imbalance in pest insects.
Use as cut flowers in a vase or bouquet
These flowers can last up to 7-10 days if you re-cut the stems regularly and keep in fresh water. Ideally, cut your flowers in the early morning. This is when they contain the highest level of moisture, so are less likely to wilt.
Choose blooms with petals that are just starting to unfold. The flowers will open fully once the stems are in water. Plunge immediately into a bucket of warm water. Strip off any leaves on the lower part of the stem that will be under the water. Decaying leaves will quickly rot and reduce the vase life of your beautiful blooms. Enjoy them in your home or grow a bunch for friends.
Resilient even in drought
Whilst cosmos seeds need water to germinate so seedlings establish, they flower even without regular watering. Perfect if you’re a neglectful plant ‘parent’ or live in a climate with little rainfall!
Medicinal Uses of Cosmos
Cosmos is a traditional medicine used in Mexico and Brazil for treating Malaria. The plant can be used as infused oil because it has anti-inflammatory and antioxidant properties. The plant also contains dimethoxychalcone, which can be used to treat illnesses such as eczema, fibromyalgia, and some viruses. It is ideal for treating skin problems and muscle aches.