How to Grow and Care For Colorful Cosmos Flowers

Cosmos spp.

“Cosmos” is the Greek word for harmony or ordered universe and is directly opposite of “chaos,” which is how one might describe the riotous explosion of color these attractive flowers bring to the home landscape.

Spanish priests in Mexico named these cheery little blooms because of their evenly placed, orderly petals.

Close up of a bright pink cosmos flower.

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Indeed, the plant’s pink, red, white, lavender, orange, or chocolate petals are beautifully spaced around a (usually) yellow central disk.

Growing Conditions

These plants belong to the huge Asteraceae family, and are cousins of daisy and marigold. Of the 20 or so species of cosmos genus, two are most commonly grown in home gardens: C. sulphureus (sulphur and yellow cosmos, Mexican aster) and C. bipinnatus (common and garden cosmos and also – because, of course – Mexican aster).

White Cosmos | GardenersPath.com
Photo by Lorna Kring.

C. sulphureus is native to Mexico, Central America, and northern South America. It has naturalized in most other parts of the world. C. bipinnatus, also native to Mexico, has found its way into most corners of the globe, as well.

Sulfur Cosmos | GardenersPath.com

These pretty flowers liberally reseed – to the point where they are sometimes referred to as weeds. In the event that you have too many blooms, cut the flowers and put them in vases.

Hot, dry conditions, along with poor to average soil, are optimum conditions for this plant. Usually grown from seed, you may also find starts at a nursery.

How to Grow Cosmos | GardenersPath.com
Photo by Lorna Kring.

In most parts of the United States, this plant is considered an annual, though gardeners in zones 9 and 10 may find them to be perennial.

And with a long growing season, they add vibrant color to the autumn garden.

Tips for Growing Cosmos | GardenersPath.com

They also make a great choice for children’s gardens and novice gardeners thanks to their easy and quick growth habits.

Recommend Cultivars

You’ll find a wide variety of cultivars and mixtures available from seed suppliers. For a brilliant red, orange, and yellow collection of C. sulphureus, try this packet of 500 seeds from Mountain Valley Seed Co., available via True Leaf Market.

Cosmos Cosmic Mix | GardenersPath.com

Cosmos Cosmic Mix

These plants will reach about 12 inches tall and produce semi-double, 2- to 3-inch flowers that bloom throughout the season.

Or, choose classic cosmos in a rainbow of colors in this seed mix from David’s Garden Seeds, available via Amazon.

Crazy for Cosmos Mix

You’ll get 10 open-pollinated varieties in this mix of 500 seeds that will grow from 45 to 54 inches tall.

David’s Garden Seeds also offers a stunning deep red variety, also available on Amazon. ‘Tetra Versailles Red’ flowers open wine-red and gradually fade to a bright pink.

Cosmos ‘Tetra Versailles’ Seeds

You’ll get 500 non-GMO, hand-packed seeds that produce 2- to 3-foot plants that bloom in about 80 days.

Want More Options?

Check out our supplemental guide: “25 of the Best Cosmos Flower Cultivars for Your Yard.”

Care and Maintenance

This low-maintenance plant tolerates fairly poor, well-drained soil with a pH between 6.0 and 8.5. You don’t want to fertilize much because you’ll end up with lots of foliage and not many flowers.

Sow seeds outdoors at a depth of 1/16 inch, or indoors five to six weeks before the expected date of last frost.

Grow Gorgeous Cosmos | GardenersPath.com
Photo by Lorna Kring.

These 1- to 6-foot-tall plants can become top heavy and floppy, so plant them in masses and they’ll support each other.

These cosmic gems flower best in full sun, but the plant will tolerate a bit of shade. It requires only a moderate amount of water.

Plant tall varieties at the back of borders or as a central focal point, and use smaller varieties as mid-sized plants in mixed beds.

A field of orange, pink, red, and white cosmos flowers in bloom.

For planters and containers, make sure to use dwarf varieties. Full sized specimens will crowd out the other plants, and their roots will dominate available soil.

Deadhead spent flowers to encourage more blooms, but leave some in place to develop seeds – they’re a favorite of visiting winter birds!

Pests and Diseases

This Asteraceae plant family member can be plagued by aphids and thrips.

For both of these pests, try insecticidal soap, such as this one from Garden Safe, available via Amazon.

Garden Safe Houseplant and Garden Insect Killer, 24-Ounce Spray

Also look out for aster yellows and powdery mildew.

The only cure for aster yellows is prevention. Use diatomaceous earth or insecticidal soap to kill the insects that spread the bacterial disease. Plants infected with aster yellows must be pulled up and destroyed.

Safer Brand Garden Fungicide, 24 Ounces

Treat powdery mildew with a fungicide, such as this one from Safer Brand, available via Amazon.

A Little Order, A Lot of Beauty

If your garden universe doesn’t include this worldly annual, perhaps it should. This easy-care plant thrives on sun and heat, offering glorious color in return.

Look for seeds online, plant indoors a few weeks before the last freeze, or outdoors in early spring. Keep diatomaceous earth and insecticidal soap on hand and you’ll be set.

Cosmos Quick Reference Chart

Plant Type: Most are annuals, self-sowing Flower Color Var. including red, pink, orange, white
Native To: Mexico, Central America, Northern South America Tolerance: Drought (when mature)
Hardiness (USDA Zone): All Maintenance Minimal; slightly invasive
Bloom Time: Summer, early fall Soil Type: Loamy, poor to average soil
Exposure: Full sun Soil PH: 6.5-7 (neutral to slightly acidic)
Time to Maturity 55-100 days, depending on cultivar Soil Drainage: Well-draining
Spacing 4-6 seeds, thin to 20-24 inches Companion Planting: Makes an excellent trap crop for aphids
Planting Depth: 1/8 inch Uses: Borders, beds, containers, cut flowers
Height: 1 - 5 feet (depending on cultivar) Family: Asteraceae
Spread: 1-2 feet Genus: Cosmos
Water Needs: Moderate Species: Cosmos spp
Attracts: Birds, bees, butterflies
Pests & Diseases: Aphids, thrips, aster yellows, powdery mildew

Are cosmos growing in your garden? In the comments section below, tell us about your experience with this galactic favorite. And learn about another Asteraceae family member in this article about Swan River daisy.

Photos by Lorna Kring, © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via True Leaf Market, David’s Garden Seeds, Safer Brand, and Garden Safe. Uncredited top photo by Lorna Kring. Other uncredited photos via Shutterstock. With additional writing by Lorna Kring.

About Gretchen Heber

A former garden editor for a daily newspaper in Austin, Texas, Gretchen Heber goes through entirely too many pruners and garden gloves in a year’s time. She’s never met a succulent she didn’t like and gets really irritated every 3-4 years when Austin actually has a freeze cold enough to kill them. To Gretchen, nothing is more rewarding than a quick dash to the garden to pluck herbs to season the evening meal. And it’s definitely time for a happy dance when she’s able to beat the squirrels to the peaches, figs, or loquats.

52 thoughts on “How to Grow and Care For Colorful Cosmos Flowers”

  1. Hello Gretchen, I love flower gardening. I always spend some time with my garden and family. I always teach my kids about gardening. You have such a beautiful garden. Thanks for sharing this post.

    Reply
  2. Hi Jane! Thank you for reading and taking the time to comment! I’m so glad you’re sharing your passion for gardening with your children…. it’s important we pass our love of the Earth on to the next generation, don’t you think?

    Reply
  3. We recently moved and I planted cosmos for the first time this spring. I now have a few, dime-sized pink blooms. The plants are only 8″ tall or so. I’ve given them no care whatsoever in the corner of our garden and though they’re tiny, they are still pretty. In WA, I remember seeing large cosmos plants with 3″ blooms. Hopefully these bitty ones will grow a bit make it through the TX summer.

    Reply
    • These flowers do love hot and dry conditions, so they should do well in your area! Keep in mind that the size of the blooms is dependent on the cultivar- different varieties may grow to a range of different heights, with blooms of different sizes as well. If you love large blossoms, try the Cosmic Mix. The Apollo, Sensation, and Double Click series are also known for large blooms.

      Reply
  4. Great article! My cosmos are coming up again this year having reseeded all over the place. I am in no way upset about that. My first year growing them, they grew taller than the house. 7ft.+, those crazy, happy, cosmos.

    Reply
    • Hi Michelle! Sound beautiful and very cottage gardenish (my favorite ornamental style…I’ve been watching too much “Escape to the Country” via Britbox).

      Do share some photos with us when they reach maturity! You can attach them to the comments using the little camera icon at the bottom of the comment box.

      Reply
  5. I have seeds and was unable to plant this last spring. The seeds are dated 2/19/19 will they be too old to plant next spring?

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  6. Thank you for your advice 😀 I am just now starting to collect these. wanted to mix them with marigold and coreopsis. you think it will be ok in the same pots?

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  7. I have a hillside too steep to mow–a hill whose wild growth the butterflies love in the fall. I thought to plant cosmos there…will scattering seeds be enough to do that?

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    • Hi Lynn; thanks for reading! Yes, that should work. Beware the birds, though! Whenever I scatter, the birds have a tasty snack and I have no flowers!

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    • HI Richard. I’m so glad you found us here at Gardener’s Path. Do you think your plants may have a fungus? You might try treating with a fungicide and see if that helps.

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  8. After 2 attempts with cosmos from store plants that failed, I started from seed this year. My plants are 3-4 feet tall with only 1 bloom????. Thought maybe the needed more water as there is brown, dying foliage at the bottom and then have also fed them twice with Miracle Grow. And now I read that they do best without this. I live in Plano and want blooms now!! Soil here is more alkaline clay. Help!!

    Reply
    • Sandy, I feel your frustration. I wonder if over-fertilization is the cause? You may just have to try again next year.

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      • You could also do a soil test. Cosmos prefers a neutral ph of 7 or a slightly acidic 6.5. If your soil is too alkaline, you could add sulfur or iron sulfate.

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  9. This is my cosmos. I planted a packet of wildflowers and these appeared. They are nearly 5ft high now. Im hoping they come back next years as they really are beautiful and very colourful and make a lovely sight all over my border.

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  10. We threw these seeds out in an area that was bare, not knowing what they would do or if they would grow. They have grown into tall, lavish flowers, the most beautiful flowers we’ve had! Super simple to grow and they grow abundantly! Love the Cosmos and will have them every year from now on!

    Reply
  11. I planted a rabbit and deer resistant flower seed mix along the fence line of our large veggie garden last year. This year nearly everything came back and the cosmos are gorgeous!
    The mix contained daisy, blanketed Susan, baby’s breath, alyssum, California poppies and more but the cosmos are spectacular and in full bloom on Sept 1st in So. Oregon garden which is visible from the street. Neighbors and passers by seem to live it as we are known as the “place with the big, beautiful garden.

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  12. Another wonderful use for orange and yellow Cosmos is as a natural dye, used with a mordant on natural fibers. The soft yellow color is beautiful!

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    • Mother Nature is mysterious, isn’t she, Jennifer? Guess your cosmos were busy concentrating underground last year so they could put on an extra-special display this year! So happy they came through for you!

      Reply
  13. Hi, I started my first planting of wildflowers this past Spring. They all have done well. I’ve been anxiously waiting for the Cosmos to bloom (it’s the middle of October in Maine). Wondered if you knew what kind and colors these might be. Also, some are upwards of 6′ tall and some are 12″ or so tall.

    Reply
    • Hi Daniel! Thanks for your comment! Wow; the Maine flowering schedule is certainly different than what I’m accustomed to here in Texas! I’m not sure I’d be able to tell what color they’ll be; I guess we’ll have to wait until they bloom! When do you get your first frost? Hope they bloom before then!

      Reply
  14. I grew lovely cosmos last growing season. I did not pull them up from the ground because my said he was going to deal with the garden beds over winter.. he didn’t though. SO.. they look pretty awful now. all gangly and falling down ( dead). Should I pull them from the ground? I assume that there will be more natural pop up’s ( reseeds).

    Thanks

    Jade

    Reply
    • Jade, can you check to see if they’re still alive (cut a stem and check for brown or green)? If they’re dead, pull them up. If they’re alive, cut them back. Either way, they do reseed easily, so you’ll likely have a fresh crop from seed.

      Reply
  15. I have partial shade, but would love to know if there is a variety that is more shade-tolerant than others. Maybe sea-shells? It’s the only one I see listed in “part shade” annual seed mixes. Not sure whether it’s just because it’s readily available or because it’s actually more tolerant of shade than say, the yellow-sulfur varieties. Thanks!

    Reply
    • Where are you gardening, Jessica? Most types of cosmos appreciate some afternoon shade in hotter regions, though they are typically “full sun” plants. It’s very difficult to get them to bloom in the shade.

      You’re right, though – I’m not sure about C. bipinnatus ‘Seashells,’ but some sources say C. sulphureus can thrive in less light, as well as being heat and drought tolerant. In Vol. 2 “Problems” of his series “What Grows Here? Favorite Plants for Better Yards” (available on Amazon), Jim Hole suggests the ‘Cosmic Orange’ cultivar.

      Reply
  16. Hi Gretchen,

    I have just been given 12 Cosmos plants which are young seedlings about 4-6 inches tall on single thin stems topped with two layers of delicate leaves.

    Do I need to pinch the top out to stimulate more growth low down, or will it develop more thickness as it grows? I am fearful they may droop when I come to plant them out.

    Please advise, thanks.

    Reply
    • Thanks for your question, Denise. Pinching seedlings back is recommended, to encourage bushy growth. Are these growing indoors? If you think there’s any chance that they may be growing leggy in an attempt to reach for the light, you might want to try adding a grow light to your setup to give them what they need in the seedling stage.

      When they grow a little more, maybe to 8 inches in height, pinch back the top 3-4 inches just above a set of leaves. Even when they are encouraged to develop a more sturdy, bushy form, cosmos may still require staking in the garden. Before planting them out, hardening them off is also recommended, to give them a few days to adjust to the outdoor conditions.

      Reply
    • Are you growing them in seed starting trays Jean, or small pots? Cosmos can be planted out any time after all danger of frost has passed. If you aren’t ready to plant them out yet, to make sure your seedlings have enough room to continue to grow, you can move them into 5-inch pots at this size, and continue caring for them indoors until they reach about 8 inches tall. At that point, you can pinch them back if you like, to encourage bushier growth. When you’re ready to transplant, harden them off for about a week, exposing them to outdoor conditions in indirect sunlight for an hour on the first day, and increasing by an hour each day that follows before transplanting.

      Reply
  17. I have yellow and orange Cosmos. Some of the flowers are double. I have bought seeds for the past 2 years with pink and white Cosmos picture on the package but they are orange when they bloom. The butterflies really enjoy them. I just want some different colors.

    Reply
    • That’s too bad, Patricia. It sounds like they were mislabeled. But at least the pollinators are enjoying them!

      We have a roundup of cosmos varieties in the works- stay tuned for suggestions this coming spring!

      Reply
    • I’m not sure exactly what you mean, ira. When you say bottom are you referring to the foliage, the stems, or the blossoms? Can you share photos? We’d love to help you with this! Perhaps this is an issue with over or under-watering, or it may just be that the flowers are finished as we come to the end of the season.

      Reply

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