Home

Cosmos

Credit: Linda Daggett
PrintPrintEmailEmail
Leave a comment
Your rating: None Average: 4.2 of 5 (38 votes)

Botanical name: Cosmos

Plant type: Flower

Sun exposure: Full Sun

Soil type: Loamy

Flower color: Red, Pink, Orange, White

Bloom time: Summer, Fall

Cosmos are annuals, grown for their showy flowers. The flowerheads may be bowl– or open cup–shaped and are atop of long stems. Cosmos are easy to grow and make good border or container plants. They make for good decorations in flower arrangements and also attract birds, bees, and butterflies to your garden.

Planting

  • If you want a head start, you can plant cosmos indoors 4 to 6 weeks before the last spring frost in trays or pots with a good seed-starting mixture. Seedlings grow fast, so move them into 5-inch pots as soon as they're 3 or 4 inches tall.
  • Plant seeds in moist, well-drained soil about 1/4-inch deep and 12–18 inches apart after the danger of frost has passed. You can also plant transplants instead of seeds. They also like soil that is not too rich.
  • They can tolerate warm, dry weather.
  • Depending on the type of flower, cosmos can grow anywhere between 18–60 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 next frost.

Care

  • In order to prolong flowering, you should deadhead the plants (remove the dead/faded flowers).
  • Because some of these plants can grow really tall, staking may be necessary.
  • Water regularly, but make sure you don't over-water the plants. Over-watering and over-fertilization can lead to plants with fewer flowers.
  • Cosmos beds may become weedy due to the fact that they self-seed, so remember to check them.

Pests

Harvest/Storage

  • 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 on good stems when they first open, they'll last more than a week in water.

Recommended Varieties

  • Picotee, which have pretty white flowers with a crimson border around the edge of the flower (some are also flecked in crimson)
  • Sea Shells, which have white, pink, or red tube-shaped petals

 

E-Cards

Send a free e-card of this charming cosmo.

 

Special Features

  • Attracts Butterflies
  • Attracts Birds

Comments

By Anonymous on May 9

CAN COSMOS BE PINCHED OUT WHEN YOUNG TO PROMOTE BUSHIER SHORTER PLANTS

By Anonymous on April 25

How much water should i give my Cosmos everyday ?

By Almanac Staff on April 26

Water only when the soil is dry and when the plants look like they need some water. Cosmos plants don't like to be wet.

By Anonymous

I have two small greenhouse kits with white cosmos I planted them a week ago and now have a dozen sprouts around 2-3 in. tall with two leefs a piece they look good but I'm finding mold is starting to grow in the moist soil should I move them to pots already or maybe leave the lids off I'm at a loss any help would be Much appreciated~arkansas

By Almanac Staff

Remove the lids and let the soil dry a bit. Air circulation will also help. The mold is not going to hurt your seedlings and may disappear with drier conditions.

By Anonymous

I've just heard that aphids will kill my cosmos and I am scared of bugs and I live in a city with lots of sun and I want to plant cosmos but I don't know where to plant it without it having aphids. I can plant it indoors(I have a sunny window),outside, or in my green house please help!

By Almanac Staff

First: if you're growing plants, you are going to encounter bugs. Before you even spot aphids, spray your plants every couple days with a few stiff sprays of water. If/once you spot aphids, just spray with insecticidal soap (soapy water) on all sides of the leaves. This should work with minor infestations before it gets out of hand. You can always resort to chemicals, but staying on top of the issue is best for you. Finally, if you notice aphids, release tons of ladybugs, our sweet beneficial insect which lives on...eating aphids! Now, ladybugs are "bugs," too. :-) In a greenhouse, they are aphid-eating machines.

By Anonymous

Thanks that help me a lot I'm just scared of most bugs that don't seem friendly and also do all cosmos get aphids?cause if some don't that'll be much easier and are they harmful to humans?

By Anonymous

Hello, I planted a beautiful Cosmos in my garden last year, it had flowers all the summer, it died off in the winter, I didn't do anything with it, will it come up again this year, or is it totally dead?

By Almanac Staff

The most common species of cosmos are annuals. The seeds need to be replanted each spring. This showy flower is easy to grow if you have full sun. Enjoy!

By Anonymous

Hi from UK. I've read your comments and now know to 'treat them tough' my question is, my seedlings after sowing in one week indoors in trays are now approximate 2" with initially leaves. I'm concerned they are bolting and are weak plants. Although theses leaves are not the true leaves can/should I repot then leaving only 1/4 showing and hope they will not be weak or will the stem rot? I intend to transplant these early seedlings to small pots in a HEATED greenhouse, it's 1'C here today. Should I start again in the heated greenhouse full light and trash these indoor seedlings?

By Almanac Staff

If the seedlings are too crowded repot them in small individual pots and then transfer them to your greenhouse. The seedlings need air circulation and not too much water. Water from the bottom if possible (make sure your pots have holes in the bottom).
Good luck!

By Anonymous

Thanks can I repot tem quite deep or will they rot?

By Almanac Staff

Cover with soil about 1/4 inch. Follow our instructions on this page for seeding.

By Anonymous

Thanks :)

By Anonymous

You say Cosmos loves hot weather and sun. I live in Az where summer temps can get from 110 to 120 at times. Is this kind of heat ok for me to put in full sun?
Thank you

By Almanac Staff

Yes, cosmos are great flowers that still bloom in AZ in the summer heat and they attract the butterflies, too. Direct seed outdoors in March.

By Anonymous

I'm looking forward to a healthy house plant to have forever. I looking forward to profuse growth of color and leaves

By Anonymous

I'm planning to grow 4 cosmos (1 in each pot) for a science experiment. It's going to have to be grown indoors, and since it's wintertime here, they won't be getting much sunlight. Would artificial light be ok for them? thanks for your help! :)

By Almanac Staff

Use a growing light and make sure the pots are in a warm area. Good luck with the experiment!

By Anonymous

I forgot to ask along with the other message, how tall and wide should each pot be? and thanks!

By Almanac Staff

If you are growing one plant in each pot they don't need to be too big. A 6-inch pot will do great. Good luck!

By Anonymous

When I purchase Cosmos from the burserty they are usually 4" tall and have strong stems. When I grow them from seeds in Jiffy Pots they grow fast and long with weak flexible stems which bruise and die when transplanted. What am I doing wrong?

By Anonymous

'burserty' sorry meant nursery

By Almanac Staff

Cosmos need a lot of sunlight to grow well. You may need more light and warmth for your seedlings to become stronger. Use a growing light placed about 6 inches above the soil if the seedlings don't receive enough sunlight.

By Anonymous

Great article, thanks for posting!

I have very limited space, so I have to grow everything in containers. How many plants per container would you advise? And what size of container? Thanks!

By Almanac Staff

You can use small to large containers. Plant 3 to 4 flowers in a small container and up to 8-10 in a bigger container. Try different varieties as cosmos come in different sizes. Make sure to remove spent flowers for a bushier growth.

By Anonymous

After the first hard freeze, do I mow down the cosmos or do I pull them out by the roots?

By Almanac Staff

Cosmos are annuals, so digging them up will be your best solution.

By Anonymous

Thank you for your reply. My cosmos have been returning every year for years so they must be reseeding themselves - is digging them up still the best solution? I have dug them up every year, but guess I am getting lazy and looking for an easier way if there is one.

Post new comment

Before posting a question, please review the page to see if the question has been asked already. Due to the volume of questions, Almanac editors can respond only occasionally, as time allows. We also welcome tips from our wonderful Almanac community!

The content of this field is kept private and will not be shown publicly.
By submitting this form, you accept the Mollom privacy policy.