Cosmos Flower Care

How to Grow and Care for Cosmos

Cosmos Flower Care-cosmos-flowering-plants
Cosmos flowers

Cosmos is native to the southwestern desert and Mexico but can be found growing in Europe and all over the United States. This low maintenance plant produces clusters of showy flowers, cosmos grows 2-3 feet tall and is in the family Asteraceae. There are dozens of cultivars of annuals cosmos but at least four species.

These garden beauties can also give your indoor living space that color pop as cut flowers, the flowers are daisy-like ranging in colors from orange, maroon, red, pink, white, yellow, purple, etc… cosmos produces nectar and pollens that attracts wildlife such as bees, birds, and butterflies along with predator insects ( hoverflies, wasps, parasitic and tachinid flies).

What I love also but cosmos is that they are self-seeding meaning once the season starts again the seeds will germinate. It’s believed that the “leaves of cosmos represent peace and love”. Cosmos will give your summer garden that much-needed flavor so continue reading to see how easy it is to grow these garden beauties.

Planting Location

When planting cosmos install in an area that gets plenty of sunlight.

Soil Type

Planting cosmos in good garden soil which has been amendment is a great way to start them of although they have also been known to grow in poor soils. If planting cosmos from seeds, the seeds should be sowed at a depth of  ¼-inch giving them a spacing of 10-18 inches.

Watering Methods

Water your cosmos regularly but don’t overwater where the soil becomes waterlogged because this will lead to root rot and other issues. Allow the soil to dry out before watering again.

Fertilizing Methods

Use fertilizers sparingly because a soil that is too nutrient-rich can produce weak plants so again keep this in mind using moderation.

Garden insect pest of cosmos

Keeping a tab on these garden insect pests will keep your cosmos in tip-top shape.

  • Thrips
  • Lygus plant bugs
  • Aphids


Thrips can cause server damage, I have had many challenging experiences with them. The adult thrips are tiny and slender, with colors of black, brown, or yellow. Their babies resemble the parents and are yellow to light green.

The damage of thrips includes white patches on the plant’s leaves along with streaks and slivery speckling this damage is caused because the fluid is being extracted from the plant by these garden insect pests. A serious infestation may also cause leaf drop, twisting of the leaves, or the leaves being deformed. The use of insecticidal soap will offer some help.

Lygus Plant Bugs

These bugs cause damage by sucking the plant’s sap or fluid, the signs to look for are insects with wings that are shaped like an x, the leaves or the foliage will have stippling or spots giving your cosmos a sick appearance. The use of insecticidal soap or horticultural oils has proven to be effective. Before applying chemicals read and follow the manufacturer’s label for best results.


Aphids are tiny pared shape insects that cause damage by sucking the plant’s fluids turning the leaves yellow followed by leaf drop. Aphids are among the easiest garden insect pests to kill. A strong spray of water from a garden hose will knock them off your cosmos eliminating them however this strong spray of water can also break the leaves of your cosmos.

The use of insecticidal soap will give good results or a homemade remedy that has proven to be effective is soap liquid and water. Add a tablespoon of soap liquid to a gallon of water shake well and apply to a 32 oz spray bottle. When applying this mixture get both the top and the underside of the leaves. Adjust the head or the spray nozzle so that this solution can come out fine and misty getting full coverage.

Coarse droppings will be ineffective, this solution should be applied on a few of the lower leaves to see if it doesn’t have an adverse effect on your cosmos, wait for at least a day or 24 hours. If there is no adverse effect then go ahead and spray the entire plant. Wait for seven days and if there are still signs of aphids then repeat the application and follow as was directed.

Diseases of cosmos

Cosmos Flower Care-bee-on-flower
Cosmos flowering plant

Keep an eye out for this disease.

  • Powdery Mildew
  • Bacterial Wilt
  • Aster Yellow
  • Canker Disease

Powdery Mildew

Powdery Mildew shows up as a white powdery coating on the plant leaves, the infected leaves will distort, turn yellow and then fall to the ground. To manage or bring this disease under control, water your cosmos in the morning to give them adequate time to dry, do not use fertilizers with high nitrogen content, and give your cosmos proper spacing for good air circulation.

Bacterial Wilt

Bacterial wilt will cause the base of the stem to get soft followed by rot, the stems and the leaves will also wilt. Cosmos that have bacterial wilt must be uprooted and discarded thoroughly, don’t replant in the same spot.

Aster Yellow

Aster yellow is most prevalent during late spring when the flower buds begin to form on the stems. Signs that your cosmos has aster yellow include your flowers, leaves, and the stems not reaching maturity along with taking on a greenish-to-yellow appearance.

This disease is encouraged during the summertime when the weather takes a turn becoming wet and cool. The leafhopper is the culprit that spreads this disease by going from plant to plant feeding. Cosmos which are infected by aster yellow must be uprooted and disposed of. Preventive measures include keeping the planting area clean of debris along with ensuring that the soil is dry and not constantly wet. When watering allow the soil to dry out between watering before giving your cosmos another drink.

Canker Disease

Canker Disease appears as dark brown scrabs on the cosmos flower stems, as the disease persists the scabs turn a dark gray, as the disease continues to take effect it will kill the top growth. The only defense is to uproot and destroy all cosmos that are infected.

Ideas where to install cosmos

Here are just a few areas to install cosmos.

1. Cosmos can be installed grouped together in a plant bed.

2. Installing them near a pond is a great idea.

3. Placing them alongside a wall will work wonders.

4. Installing them alongside a fenced area is the right place for them.

5. What about an area alongside your pool?

6. Plant them around the trunk of a tree.

Deadheading Cosmos

Deading heading cosmos is a great way to improve their appearance along with increasing their flower production. The method of deadheading involves the removal of spent or faded flowers when this happens your cosmos will shift their energy from setting seeds to producing more flowers.

When deadheading or pinching your cosmos hold the stem firmly below the flower head and remove the flowers which are faded. When working on a plant bed that has many cosmos remove spent flowers with a hedge shear that is sharp.

The final word

So what do you think about these babies, are they worth your time? I think so, these garden beauties have proven to work wonders and will take your garden and landscape up a notch. Why not join the many homeowners that are taking advantage of these plants which are truly game-changer? with that said let’s get started on installing them.


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About the author

+ posts

Norman loves being in the garden, both at home and for his job....
he is 'Natures Little helper' being outdoors, growing his vegetables and flowers from an early age.
Now having spent over 22 years in the profession he want to give some of his knowledge to others...
his vast array of hints and tips you will find scattered over this site will help you no end growing plants in your garden.

11 thoughts on “Cosmos Flower Care”

  1. These are beautiful flowers and would look gorgeous in my front yard however I have absolutely no shade.  How will they do in extreme heat and sunlight in Texas summer weather? Do I need to be concerned about that?  I do water to keep everything alive and to keep the foundation of my house from cracking so they would get that.

    • Cosmos loves the full sun, Texas is pretty hot so what I would advise is that you give it a test run and install some and see what happens also implement the tips which I have laid and please let me know how it goes. All the best to you and have a good day.

  2. Hi Norman,

    Thank you for this wonderful article. I found it quite educational, because I was not familiar at all with the Cosmos Flower. That could be because I live in the USA. Are these flowers available here?

    I raised vegetables in many home gardens and I am familiar with the problems of pests like aphids, and tripes! The stink bug is a problem here now! I also like to have a praying mantis or two and some ladybugs in my garden! They feast on the bad bugs! 

    I have used the horticultural oils at times, when things get bad, and also Rotone(a pesticide made from ground up flowers) and had success with that. Since, I was eating the vegetables, I wanted to use the safest chemicals possible, so soapy water on the underside of the leaves, the manner you mentioned, worked well also!

    Thanks for the great information!


    • Hello, Chas so happy to meet you, you seem to have a wealth of knowledge in this field also.  I am so happy that I could help all the best to you and wishing you continued success in your field of work.

  3. Hi there, I want to attract wildlife to my garden once it has all finished and I get all the right flowers planted but you say the Cosmos are native to Mexico so would they grow anywhere else, like the UK for instance?

    These would look gorgeous just dotted around the garden looking like they have been growing wild, especially both the white and purple Cosmos, rather than planted like a row of soldiers, Wouldnt They?

    I would be so devastated if you said the Cosmos won’t grow in the UK because now I have seen them I really want them growing in my back garden now

    Please tell me they will, lol.

    • Hello so happy to see you again. Cosmos are really amazing an can do wonders. As long as you give them sufficient sunlight and follow the care of them as laid out in my post you will be just fine. All the best to you and have a good day.

    • Hello, Matthew so glad to see you and hope all is well cosmos are pretty amazing plants and can really lighten up your garden area. These garden beauties have so many benefits. Not to worry my friend as long as they are getting sufficient sunlight along with following the tips that I laid out you will be smiling from ear to ear. Please let me know how it goes my friend so happy to see you again and wishing you all the best of success.

  4. wow! I love the colors on your site! Not only did I feel like I was learning about things that I already knew, but I enjoyed doing so regardless. Your site made me feel like I was there enjoying the day with you. I love that you have gone further to teach us about everything rather than the basics. I can tell you really love what you do! Hope you are well…Glenn

  5. Just been reading your article and found it a great read. Personally, I haven’t had a garden for about 20 years, and would probably be useless at flowers if i did. But I still love to read about a good garden and love to see the work put into other peoples gardens. Thnks for sharing


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