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Cosmos flower seedlings


How to Grow and Care for Cosmos

Cosmos are freely flowering annuals that are easy to grow by sprinkling some seeds in the garden after any danger of frost has passed. These quintessential cottage garden flowers reach full maturity in about two months. Cosmos can be slower to germinate, but it blooms quickly after that and continues to flower through the fall. The flowers sit atop long slender stems and form a cloud of attractive color all summer that attracts bees, butterflies, and birds to your garden. Cosmos flowers look a lot like daisies. They come in a broad range of colors, with more cultivars developed every year. The leaves grow opposite on stems and are deeply lobed, pinnate, or bipinnate and feathery-looking depending on the type. If you plan to have cosmos and live in the southern U.S., consider keeping them as potted plants since they tend to be invasive there.

Common Name Cosmos, Mexican aster, cut-leaf cosmos
Botanical Name Cosmos sulphureus, Cosmos bipinnatus 
Family Asteraceae
Plant Type Annual
Mature Size 1-6 ft. tall, 1-3 ft. wide
Sun Exposure Full
Soil Type Well-draining soil
Soil pH 6.0–6.8 (Acidic)
Bloom Time Summer through fall
Flower Color Golden yellow, white, pink, magenta, orange, yellow, red, chocolate
Hardiness Zones 2–11 (USDA)
Native Area northern South America, Central America, and southern North America

Cosmos Care

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.

Warning

Cosmos sulphureus is invasive in the southeast United States. Check with representatives from your local extension office to learn about any restrictions in your area.

​The Spruce / Letícia Almeida  Tim Bird / Getty Images  The Spruce / Letícia Almeida

Light

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.

Soil

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.

Water

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.

Fertilizer

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.

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 to USDA zone 7, but it is higher maintenance than annual cosmos. Like dahlias, it grows from tubers.

Other common cosmos cultivars include:

The Spruce / Letícia Almeida Eva Lechner / Getty Images Suzanna Ruby / Getty Images

Pruning

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.

Propagating Cosmos

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:

  1. You'll need sterile pruning shears or scissors and a pot of sterile, well-draining potting soil.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

How to Grow Cosmos From Seeds

Start seeds indoors, four to six weeks before the last frost. Or if you can sow cosmos outdoors directly in the garden well after the threat of frost is gone. Cosmos grow very quickly but can be killed by a late frost, so don't rush it. They typically germinate in 7 to 21 days at 75 degrees Fahrenheit, followed by flowering in about 50 to 60 days.

Loosen the soil to a depth of 8 inches. Plant the seeds and cover them with 1/4 inch of fine soil. Seed packets usually recommend precise spacing, such as at 2-foot intervals, or you can scatter the seeds and let the plants support each other as they grow. You can always thin them out later, moving the extra plants to another part of the garden.

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.

Overwintering

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.

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.

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.

FAQ

Article Sources

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Cosmos sulphureus Cav.sulphur cosmos. United States Department of Agriculture.

  2. Cosmos (Cosmos). Connecticut State Agricultural Experiment Station.

  3. Cosmos bipinnatus. Missouri Botanical Garden.

  4. Fusarium Wilts. Royal Horticulture Society.

  5. Diseases of Cosmos. National Gardening Association.

  6. Powdery Mildew. University of California Integrated Pest Management.

  7. Cosmos: Aster Yellows. University of Minnesota Extension.

How to Grow and Care for Cosmos Flowers

Cosmos spp.

Cosmos flowers are gorgeous ornamental plants that flourish in less than ideal conditions.

A boon to pollinators and other beneficial insects, these plants are a welcome addition to both the flower bed and the organic veggie garden.

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

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When I create my summer garden, I like to add elements that make it feel like a peaceful oasis and that are very low maintenance.

Cosmos flowers fit both of these requirements perfectly – they don’t require much care, but wow, do they ever make the garden feel like a haven of life and beauty!

In fact, one of my favorite ways to relax on summer days is to watch bees, butterflies, and even hummingbirds foraging from the showy blooms on my cosmos plants.

Sweetening the deal, these gorgeous flowers produce loads of blooms from early summer all the way up until the first fall frost.

In this article you’ll learn everything you’ll need to know to grow these lovely flowers – so that, if you choose, they can become one of your summer highlights too.

Here’s what we’ll cover:

What You’ll Learn

What Are Cosmos?

Cosmos are herbaceous plants cultivated for their gorgeous flowers. They’re most often grown as summer annuals.

These flowers are available in a wide assortment of cultivars comprising many different colors and featuring different types of blooms.

Blooms are held on tall, branching stems, while flowers have petals in shades of pink, purple, white, lavender, red, orange, or yellow, as well as bicolors, which are beautifully spaced around a central disk.

Of the 20 or so species in the Cosmos genus, two of these are commonly grown in home gardens.

C. bipinnatus. Photo by Lorna Kring.

C. bipinnatus, also known as “garden cosmos,” is most often sold in a mix of white, pink, purple, and burgundy. The foliage is delicate and wispy, and bloom colors tend toward cool shades.

C. sulphureus, also known as “sulfur cosmos,” comes in warm shades of yellow, orange, and red and has foliage that you might mistake for marigold or chrysanthemum leaves.

C. sulphureus.

A third species that is somewhat less common in the garden landscape is C. atrosanguineus, also known as “chocolate cosmos.”

You’ll learn more about these species and their cultivars – as well as some tips on where to purchase them – later in this article, so keep reading!

Cultivation and History

Plants in the Cosmos genus are native to the Americas, ranging from Washington State in the Pacific Northwest of the United States all the way to South America.

However, the three species most commonly cultivated in gardens are all native to Central America.

These plants belong to the huge Asteraceae family, and are related to other garden beauties such as coneflowers, dahlias, and marigolds.

The genus Cosmos takes its name from the Greek word “kosmos,” a word with many different translations, ranging from “adornment” to “universe.” In the case of this flower, the word is best translated as something akin to “beauty.”

These lovely flowers have been used and enjoyed by humans for many centuries, if not longer.

According to T. K. Lim, author of “Edible Medicinal and Non-Medicinal Plants,” Volume 7, which is available on Amazon, pre-Columbian civilizations in Latin America used the orange or yellow flowers of C. sulphureus to produce dye.

Later, explorers imported cosmos seeds into Spain, and in the late 1700s, botanist Casimiro Gomez de Ortega brought C. bipinnatus from Spain to England.

Although they are most commonly referred to by their genus name, these flowers are also known by the common name “Mexican asters.”

In most parts of the United States, Mexican asters are considered annuals, though gardeners in USDA Hardiness Zones 9 and 10 can treat them as perennials.

Propagation

You can propagate garden and sulfur cosmos by sowing them directly into the soil, or by starting them indoors and transplanting out the seedlings. For chocolate cosmos, the most reliable propagation method is to divide tubers.

Outdoors from Seed

Garden and sulfur cosmos are extremely easy to grow from seed, so if you are a beginning gardener (or just revisiting some of the basics) these are excellent flowers to start with.

In fact, these seeds germinate so easily that they tend to self-sow, growing back from seed year after year, and they are known for becoming a bit weedy.

(However, I must point out that a plant’s status as a “weed” is entirely up to one’s point of view. I look at cosmos volunteers not as “weeds” but as welcome “bonus” blooms.)

Does it sound like I’m digressing? I’m trying to make a point about growing these flowers from seed, and you’ll see where I’m going in just a moment, so bear with me…

Before you start sowing, you’ll want to know the best time to plant these seeds.

And now we’re coming to the point. Every other source you consult will most likely recommend waiting to sow cosmos seeds until after the last average spring frost for your location.

However, I’m not one to follow horticultural advice to the letter while ignoring what’s transpiring in my own garden, or the veggie plots and flower beds of many other gardeners.

The number of volunteer cosmos seedlings that sprout before the last spring frost every year and survive to brandish their glory throughout the summer are proof that waiting may not be necessary.

Taking a cue from what was happening among my volunteers, lately I have started sowing these seeds in early spring along with my cool-weather crops, just to see what would happen.

As I suspected – and much to my delight! – my early-spring-sown seedlings survive light frosts, providing me with early summer blooms, a valuable asset in my region where the growing season is short.

I’ll admit, though, that I consider this approach to sowing warm-season flowers to be an experiment.

So if you want to play it safe, wait until one to two weeks after your last average frost date when the temperature of your soil has reached at least 60 or 70°F.

If you’re willing to take a risk, try planting some of these at the same time as your spring garden seeds. You can always use floating row covers to protect the seedlings if your weather forecast predicts a hard freeze.

When you’re ready to sow, prepare your beds by mixing in some compost, push aside a little soil to use for covering the seeds, then smooth the soil down so it’s level.

Water the soil in with a gardening wand so the soil surface is moist.

Place a group of three seeds every nine to 12 inches, then cover them very lightly with soil. The seeds should only be covered by about 1/16th of an inch.

Expect seedlings to emerge in five to 21 days after sowing.

While the seeds are germinating, keep the soil moist, watering daily if needed.

Taper off the frequency of your watering as the seedlings that sprout become established. You’ll learn more about how often to water established plants later in this article.

When the seedlings are a couple of inches tall, thin them so you have only one every nine to 12 inches.

Those of us in colder zones where the ground stays frozen throughout winter might also try pre-seeding our gardens with cosmos seeds in the fall or sowing them in the winter so they come up the following spring.

Both of these methods will expose young seedlings to early spring frosts, so keep your row covers at the ready in case any hard frosts are forecasted.

Indoors from Seed

If the early sowing method I just described sounds a little too risky for your taste but you still want to get a head start on summer, you can sow these seeds indoors and then transplant them out after your last spring frost.

You’ll want to get the timing right when using this method so you don’t end up with plants that are too big to manage indoors when the weather is still frigid outside.

Plan to sow seeds indoors four to six weeks before your last average frost date.

For indoor sowing, you’ll need a sterile seed-starting medium, two-inch pots or six-celled seed starter trays, a spray bottle, and of course, seeds for the varieties of your choice. You may also want to use a grow light and a heat mat.

Fill the pots or cells with growing medium, leaving about half an inch to an inch of space between the surface of the soil and the rim of the pot. This way, you’ll have room to water without spilling soil over the edge.

Spray the growing medium with water to moisten it without allowing it to become soggy. Place one to three seeds in the center of the pot or in each cell, cover them very lightly with soil, then spray the surface of the soil with the water bottle.

If you have a very bright south-facing window, you can grow your seedlings next to this light source. Alternatively, you may want to consider using grow lights, which will give the seedlings the light they need and prevent them from becoming leggy.

If using sunlight as a light source, rotate the pots daily to prevent lopsided growth.

Keep the surface of the soil moist, watering daily with your spray bottle if needed.

Ideally, keep the seeds warm while they’re germinating, at a temperature of at least 60°F.

Jump Start Heat Mat

To keep them warm, try using a heat mat, such as the Jump Start heat mat, available for purchase in a few different sizes on Amazon.

Look for seedlings to emerge anywhere from five days after sowing up to 21 days.

Once the seedlings size up and when the soil begins to dry out more quickly, switch from watering with a spray bottle to using a houseplant-adapted watering can, which will provide good control over where the water flows.

If more than one seedling has germinated in each pot or cell, thin the weakest-looking seedlings by snipping them off with a pair of scissors.

You can transplant the seedlings one to two weeks after the last frost, but be sure to check your weather forecast first for any dips in the temperature.

While direct-sown seeds may have some resistance to light frosts, don’t count on that protection for seedlings grown indoors. These hothouse flowers will be much more vulnerable and not yet able to put up with extreme weather fluctuations.

Harden seedlings off before transplanting to help them build up some resilience.

You can find guidance on hardening off and planting transplants in our complete guide to starting annuals indoors.

From Division

Propagation via division is only appropriate to use for C. atrosanguineus, the species commonly called “chocolate cosmos,” which doesn’t grow reliably from seed.

To divide this species, you can follow the same procedure as you would for dividing perennials.

You can learn more about the propagation of C. atrosanguineus, as well as specific growing and care recommendations, in our complete guide to growing chocolate cosmos. (coming soon!)

How to Grow

This summer annual is easy to grow and doesn’t require any coddling. In fact, giving it too much love might cause problems.

Here’s what you need to know in order to provide these flowers with the best possible care:

Sun

These plants should be grown in full sun. That’s to say, they should receive at least six to eight hours of direct sunlight.

If summer heat is extreme in your location, a bit of shade can help, particularly afternoon shade. Just make sure that they get their full quota of sunlight.

Water

When seedlings are young, they will require more frequent watering.

However, once plants are established, they have only moderate water needs, with sulfur cosmos requiring even less water than other varieties.

In fact, overwatering can result in plants with fewer blooms.

So when it comes to irrigating these flowers, water infrequently but deeply, preferably showering the surface of the soil rather than the tops of the plants in the absence of rain.

These annuals are fairly drought tolerant, but during hot summer weather, look for wilting as a sign to increase watering.

Soil

These low-maintenance plants grow best in sandy or loamy soil with a pH ranging between 6.0 and 8.0. The soil should have excellent drainage.

Overly rich soil can cause plants to become leggy and droop over, so this is truly a case where too much love won’t win you any favors.

Growing Tips

Pruning and Maintenance

Cosmos plants require very little maintenance, especially if you don’t mind seeing dead flower heads mixed in among the blooms. Here’s what you need to know:

Weeding

While young plants are getting established, weeding around the small fern-like seedlings can help so they won’t be crowded out.

If weeding seems to take up too much of your gardening time, be sure to read our article on how to spend less time weeding.

However, keep in mind that once cosmos are well-established, they won’t be impacted as much by neighboring weeds.

Fertilizing

Fertilizing is another point where too much love can cause problems for these members of the aster family.

Giving them too much help in the way of fertilizer can make them overly tall and lanky.

Instead of fertilizing them during the growing season, just mix some compost into the soil before you sow your seeds or set in your transplants, and your fertilizing is done!

If you offer these plants nothing but compost, they’ll be fine. But if you introduce any other amendments, be aware that fertilizers heavy in the plant nutrient nitrogen will encourage the production of foliage, but not flowers.

Mulching

Mulching around these annuals will help prevent water loss from the soil and extend the time in between watering visits.

Place mulch about two to three inches thick, taking care to leave a couple of inches bare around the stems of these plants, to avoid creating conditions where fungal pathogens could flourish.

And when it comes to mulch, think beyond wood chips and pine straw – there are many other options you can use to cover the soil. Check out our article on mulching to learn more.

Pruning

Cosmos don’t require pruning, so if you are taking a low-maintenance gardening approach like I am, you can skip this part.

However, if you prefer the look of smaller, bushier plants, these can be cut back to a third of their height in midsummer. Just be sure to use sterilized garden pruners to avoid unintentionally spreading disease between plants.

Another reason you might want to do a bit of pruning is if you want to keep spent flower heads off of your plants.

Cosmos seed head.

Personally, I love seeing these plants with flowers at all stages of their development – new buds, opening blooms, glorious flowers, and fading petals, finally turning into seed heads.

However, if you don’t like seeing the spent heads or want to prevent re-seeding, you can deadhead them by snipping the faded blooms off with a pair of scissors or garden snips.

Staking

When grown densely in mass plantings, these annuals won’t need any help staying upright – each flower’s neighbors will provide structural support to help keep it from leaning.

However, if your plantings aren’t quite dense enough to offer structural support, you may want to consider staking these plants.

It’s best to provide support before the plants are eight to 10 inches tall, so you don’t damage their root systems when inserting stakes into the ground.

If you only have a few cosmos plants, you can support each one individually with a bamboo stake and some twine.

However, if you have a large planting of these flowers, you may want to use a staking system similar to that used for tomatoes, such as the Florida weave.

You can read our article to learn how to create your own Florida weave.

Species and Cultivars to Select

As mentioned earlier, there are three main species of Cosmos available to gardeners. We’ll look at the features of each of these, consider their differences, and explore a few cultivars of interest.

Atrosanguineus

Commonly known as “chocolate cosmos,” C. atrosanguineus is a species native to Mexico that has dark, brownish-red blooms with even darker centers.

True to their common name – yes, it’s true! – these one-and-a-half-inch flowers have a chocolatey fragrance. Blooms are single, making them friendly to pollinators.

C. atrosanguineus.

The leaves are small and lance shaped, and the flowers are held on long stems above the foliage, making them wonderful for cut arrangements.

These plants have a mounding growth habit, growing up to 30 inches tall with an 18-inch spread.

Since most varieties of this species don’t have seeds that will germinate reliably, they are typically grown from tubers instead.

C. atrosanguineus is often grown as an annual in Zones 2 to 6, but the tubers can be lifted and stored like dahlias for the winter.

Grown as a perennial in Zones 9 to 11, C. atrosanguineus sometimes survives the winter in Zones 7 and 8 too, if well-mulched.

If you decide to try growing this species from seed, look for the ‘Black Magic’ cultivar. It has viable seeds, but you should expect very low germination rates nonetheless.

Better yet, purchase tubers or live plants to ensure your success.

‘Choca Mocha’ is a petite cultivar of C. atrosanguineus that grows up to 12 inches tall and wide.

‘Choca Mocha’ Live Plant

You can purchase a live plant ready to transplant into your garden via Burpee.

Bipinnatus

C. bipinnatus is the flower most gardeners tend to think of when they hear the word “cosmos.”

Often referred to as “garden cosmos,” this native of Mexico has wispy, threadlike foliage and flower heads that are two to six inches wide.

Cultivars of this species are available in a huge range of cool-toned colors, including shades of pink, purple, burgundy, yellow, and white.

C. bipinnatus. Photo by Lorna Kring.

In addition to this wide range of hues, some intriguing varieties are even bicolored.

Some cultivars have single flowers with wide open petals, while others bear frilly, semi-double flowers, and still others have deeply ruffled double blooms. All of them are magnificent in cut flower arrangements.

Depending on the variety, plants can grow up to six feet tall.

One of my favorite varieties of C. bipinnatus is ‘Versailles Tetra Red.’ This burgundy-hued cultivar reaches up to four feet tall and has two-and-a-half-inch blooms.

‘Versailles Tetra Red’

You can purchase ‘Versailles Tetra Red’ in packages with enough seeds to cover 80 square feet at Eden Brothers.

Sulphureus

C. sulphureus has a widespread native range across Central America.

Commonly known as “sulfur cosmos,” these usually grow one to three feet tall with a two- to three-foot spread, but some varieties can reach six feet tall.

Blooms are two to three inches wide in shades of red, yellow, gold, and orange. And like milkweed, they attract monarch butterflies.

C. sulphureus.

Compared to C. bipinnatus and C. atrosanguineus, sulfur cosmos have shorter stems, making them less desirable as cut flowers.

The branching stems have an open, sprawling growth habit and foliage is green with leaves that are four to eight inches long.

Also known as “yellow cosmos” and “klondike cosmos” the leaves of these plants look similar to marigold or chrysanthemum foliage, and they are not as wispy as the leaves of C. bipinnatus.

‘Diablo’ is a fiery cultivar of C. sulphureus that bears bright, one- to one-and-a-half-inch, reddish-orange blooms on four- to five-foot plants.

An outstanding cultivar, ‘Diablo’ won an All-America Selections award in 1974.

‘Diablo’

If you’d like to add this warm-hued cosmos variety to your garden, you can find ‘Diablo’ in packets of sixty seeds from Botanical Interests.

Want More Options?

This selection of varieties is really just scratching the surface of the myriad of options available. If you’d like to explore more wonderful cultivars, make sure to check out our supplemental guide to 25 of the best cosmos flower cultivars to plant at home.

Also be sure to check out our guide to harvesting and saving cosmos seeds.

Managing Pests and Disease

One of the best features of resilient cosmos plants is that they aren’t often troubled by pests or diseases. You can also count them among the many deer-resistant landscaping options you might want to consider.

Here’s a look at some of the pests and ailments you are most likely to encounter:

Pests

Mexican asters are generally pest free, and you are not likely to encounter a problem. However, it’s always good to know what to be on the lookout for in case pests do move into your flower patch.

Aphids

If you notice ants crawling all over your cosmos flowers, take a closer look and see if you spot any aphids as well.

While the activity of the ants will be fairly obvious, the aphids may be harder to spot. Ants collect honeydew from aphids, which is why you might find both insects living on your plants.

Check stems and the undersides of leaves for aphid populations.

Luckily, cosmos also attract beneficial insects such as green lacewings, whose larvae are voracious predators of aphids.

Make sure you know how to recognize beneficials like green lacewings, so you don’t mistake them for problem insects.

If your garden is lacking in beneficial insects, you can purchase green lacewing eggs to help control an aphid infestation. Once the eggs hatch, the larvae will begin to feed on soft-bodied insects such as aphids.

Green Lacewing Eggs

You can find green lacewing eggs for purchase in a selection of different quantities from Arbico Organics.

When using beneficial insects as a biological control, be sure you aren’t defeating the purpose of your efforts by applying broad range pesticides.

Want to learn more about deterring and eliminating these pests? Check out our complete guide to controlling aphid infestations.

Spider Mites

If you notice yellow stippling of your plant’s foliage, check the undersides of the leaves – your plants might have spider mites.

When infestations are severe, you might also notice webbing around the foliage.

These small arachnids suck nutrients from plants and can cause stunting.

You have many options for dealing with such an infestation – learn more about detecting and controlling spider mites in our article.

Thrips

You’ll be most likely to see thrips feeding on flowers rather than foliage.

Thrips feed on a flower.

These insects are so small that you’ll need a hand lens to properly identify them.

While thrips won’t cause much direct damage to your plants, they can transmit viruses which can cause a lot of harm.

Learn more about identifying and controlling thrips in our guide.

Disease

You aren’t likely to find signs of disease among your cosmos, but in the rare event that you do, here are some the most likely problems you might encounter:

Aster Yellows

If your cosmos are infected with aster yellows, you’ll most likely notice deformed flower heads on your plants.

These deformations are caused by phytoplasmas spread by an insect, the aster leafhopper.

Since the only cure for aster yellows is prevention, it can be helpful to know what to look for and what steps to take to prevent it.

To learn how to prevent this disease as well as how to manage an existing infection, check out our article on aster yellows.

Powdery Mildew

Have you noticed large white or gray patches on the foliage? If so, powdery mildew may be to blame.

While patches of mildew on leaf tops are the first sign, affected leaves will eventually turn brown and shrivel up.

Risk of encountering this fungal disease is highest when the weather is humid at night and less so during the day. If you live in a humid climate, you can help prevent this disease by ensuring there is adequate airflow around your plants.

If infection has already set in, remove any infected leaves and dispose of them to prevent further spread.

Read our article to learn more about how to prevent powdery mildew, as well as how to and treat it using natural, homemade remedies.

Smut

Smut, another fungal disease, can make itself known in your ornamentals with the appearance of small yellow spots on foliage.

These spots will develop into pustules that eventually rupture, spreading fungal spores.

Smut is best prevented through good gardening habits such as allowing adequate spacing between plants, watering the soil surface instead of showering the tops of plants, and taking care to sanitize garden tools between uses.

You can learn more about smut in our article.

Best Uses

Cosmos can be used in the landscape in countless ways.

Use them as part of your landscaping plan for a tall, wispy floral accent or create mass plantings for a strong visual statement.

In mixed flower beds, plant tall varieties at the back of borders or as a central focal point, and use smaller varieties in the midground or foreground.

Photo by Lorna Kring.

Taller varieties can also be used to create a vegetative screen.

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

Since they are easy to grow, these are a great option for children’s gardens, and they are also a welcome addition to butterfly gardens or cut flower gardens.

In the veggie garden, cosmos make valuable insectary plants to attract beneficial insects such as bees, predatory wasps, and hoverflies – and they can be grown as companion plants among vegetable crops such as artichokes, cabbage, or kale.

Blooming right up until the first frost, and sometimes longer, these flowers are excellent for late summer color.

Quick Reference Growing Guide

Plant Type:Herbaceous flowering annualFlower/Foliage Color:White, red, pink, purple, yellow, orange/green
Native to:Central AmericaMaintenance:Low
Hardiness (USDA Zone):2-11 (some varieties perennial in 9-11)Tolerance:Moderate drought tolerance when mature
Bloom Time:Summer to fallSoil Type:Sand or loam
Exposure:Full sunSoil pH:6. 0-8.0
Time to Maturity:60-90 days, depending on varietySoil Drainage:Well-draining
Spacing:9-12 inchesCompanion Planting:Black-eyed Susans, coneflowers, dahlias, hollyhocks, marigolds, ornamental grasses, sweet peas, zinnias
Planting Depth:1/16 inch (seeds), depth of root ball (transplants)Uses:Butterfly gardens, children’s gardens, companion planting, cut flower gardens, insectaries, mass plantings, meadows, ornamental landscaping, pollinator gardens, vegetative screens
Height:1-6 feetAttracts:Bees, birds, butterflies, hoverflies, wasps
Spread:1-3 feetFamily:Asteraceae
Water Needs:ModerateGenus:Cosmos
Pests & Diseases:Aphids, four-lined plant bugs, Japanese beetles, spider mites, stalk borers, thrips; Aster yellows, bacterial wilt, botrytis blight, leaf spot, powdery mildew, smutSpecies:Atrosanguineus, bipinnatus, sulphureus

A Vision of Universal Beauty

We’ve covered all the basics of growing beautiful cosmos flowers, so how about a quick recap?

Grow these lovelies in full sun and in well-draining soil, water them judiciously, don’t over-fertilize – and be sure to take advantage of the many options available when growing cosmos from seed!

Are cosmos growing in your garden? Tell us about your experience with this flowering favorite in the comments section below.

And to learn about other annual flowers for your garden, check out these articles next:

planting seeds, home care

Kosmeya has long been loved by summer residents and gardeners for the beauty and elegance of its flowering, unpretentiousness and simple cultivation techniques. The seeds of this crop germinate well and when sown in open ground, the procedure can be carried out during May. But growing cosmos through seedlings allows you to see flowering a little earlier, and you can also control the process of growth and development of seedlings.

Contents

Brief information about cosmea

The charming cosmea has other names: Cosmos, Moscow chamomile, disheveled young lady. nine0003

The most popular type of this crop: Cosmea Double-pinnate (and its hybrids). Shown in the photo below. The species is annual, has a height of about 0.8-1.5 m. The inflorescences have a diameter of about 10 centimeters.

Other types of cosmea are also grown, but they are less popular: Terry cosmea (annual), Sulfur-yellow (annual), Chocolate (perennial).

The flowering of the one-year-old cosmea is absolutely charming! Its inflorescences are distinguished by their delicate, openwork beauty. They can have pink, white, red, purple and other shades of white-red palette. The main features of this plant: space is very unpretentious and drought-resistant. nine0003

Moscow chamomile has the ability to self-propagate through self-seeding. The gardener is only required not to pluck the faded inflorescences so that the seeds can safely fall to the ground.

Cosmos can be tall, medium or short. However, tall and medium plants are most common. Therefore, be sure to pay attention to the information on the package in order to buy a variety with the optimal height.

Annual blooms, usually from July until frost. But growing through seedlings allows you to see flowering a little earlier. nine0003

To get the most out of the gentle beauty of the cosmos, you need to choose a suitable landing site. The plant grows well and blooms exclusively in sunny areas. It is also desirable that the location is protected from the wind. The soil should be loose, light, moderately nutritious. Do not plant a plant in areas with shading, stagnant moisture, heavy soil.

When to plant cosmea for seedlings at home

Seedlings of the culture develop very quickly, so do not rush to sow, otherwise the plants will outgrow by the time they are planted in open ground. It is optimal to plant cosmea seeds for seedlings at the end of March or at the beginning of April . In different regions, the sowing dates are slightly different: in the Moscow region you can plant at the end of March, in Siberia, in the Urals - in the first or second decade of April, but in the south you can already plant a crop in early March.

By the way! Lunar calendar 2022 will help you choose the most suitable landing dates:

  • Auspicious days:
    • in January: 1, 10, 11, 15, 16, 19, 20; nine0010
    • in February: 7, 8, 12, 13, 14, 15;
    • in March: 10, 11, 15, 20, 21, 24, 25.
  • in February: 1, 16;
  • in March: 2, 16, 17, 18, 31.

Features of preparation for sowing cosmea for seedlings

Before planting flower seeds, it is necessary to prepare for the event. Features of the preparation are as follows:

  • The choice of a suitable container is unequivocal - it is better to immediately plant cosmea in individual containers (cups, pots, plastic cassettes, peat tablets). Sowing in individual containers will allow you to avoid picking and save your time, you can immediately plant seedlings in open ground using the transshipment method. It is also very important that there are drainage holes at the bottom of all containers (except for peat containers, the material perfectly passes excess moisture without holes).

  • Soil mix must meet the following characteristics: loose, nutritious, light, air and moisture permeable. Cosmos seeds can be sown in ordinary flower seedling soil, which can be bought at almost any garden center or store. You can also prepare the soil with your own hands, for this the following components are mixed: lowland non-acidic peat (2 parts) + garden soil (1 part) + sand (1 part) + humus (0.5 parts).

  • As a preparation, it is recommended to decontaminate the soil mixture . It is better to do this 1-1.5 months or at least a week before the procedure. For disinfection, you can ignite the earth in the oven or steam it.
  • Seeds can be harvested or purchased. Since garden culture is very popular, you can buy space seeds in almost any country store. As for the preparation of seeds, processing can be omitted, cosmea seed has good germination. nine0010

Scheme of planting seeds of cosmea for seedlings

If you have done everything described in the paragraph above, then the matter remains completely small. Sowing this crop is extremely simple. So, step-by-step instructions for planting cosmos for seedlings:

  • Step 1: Fill all cups, pots or cassette cells with soil.
  • Step 2: Place one seed in the center of the container. And it’s even better to put 2-3 seeds so that you definitely have at least one seedling growing, in case the others do not germinate. nine0010
  • Step 3: Lightly press the seed into the ground with your finger.

Important! Cosmea seeds germinate in the light, so the sowing is superficial, you can not fill them up or bury them.

  • Step 4: Moisten the soil with a fine mist sprayer. At the same time, the water should be a little warm, and always clean and settled!
  • Step 5: Cover each container with a lid or plastic wrap.
  • Step 6: Place the containers in a sunny place with a temperature of 15-18 degrees Celsius.

Please note! You can also sow cosmea seeds in a common wide and shallow container. With this sowing, the distance between the seeds should be maintained - 5 centimeters. When 2 true leaves appear, picking into separate cups will be required.

Care of cosmea seedlings at home

Under favorable conditions, cosmea seeds germinate in 1-1.5 weeks. Therefore, for friendly and good shoots, you need to provide all the necessary growing conditions. But proper care is also important at the stage of growing cosmea seedlings before planting in the ground. nine0003

Care must be taken according to the following algorithm:

  • Before germination, all containers must be covered with a film or lid, it is necessary to air them briefly daily, removing the cover. After the emergence of shoots of space, the covers and films are removed forever.
  • Particular attention should be paid to the temperature regime. In warm conditions, cosmea seeds germinate worse, therefore, for successful germination, it is necessary to provide a temperature in the region of + 15-18 ° C. This t must be maintained in the future. nine0010

  • Immediately after sowing, place containers on the sunniest window sill, seeds need light to germinate. In the future, full lighting is also necessary. If there is little sun, it is recommended to turn on phytolamps.
  • If you planted several seeds in one cup, then when shoots appear, you will need to leave one of the strongest seedlings, and pinch the rest at the base.

  • Cosmea seedlings are watered carefully, as the top layer of the earth dries up. It is impossible to allow the earthen coma to dry out or flood the earth too abundantly (otherwise, mold and fungal diseases can be provoked). nine0010
  • When pulling out seedlings of cosmea, it is necessary to correct the growing conditions: improve lighting, lower the temperature. As a last resort, you can pinch the top, but this procedure will delay flowering.

How and when to plant seedlings of cosmea in open ground

Siberia, in the Urals - at the end of the month). The most important thing is that after transplantation, return night frosts do not return. The weather should also be consistently warm. nine0003

It is recommended to harden seedlings 2 weeks before planting. Thanks to this, it adapts better, takes root in a new place, and will be more resistant to bad weather. At first, you can simply put the seedlings in a cooler room, often ventilate. Then it is optimal to take the plants outside (to the garden, to the balcony) starting with a small amount of time and gradually increasing it.

At the chosen place in the garden, it is necessary to make holes at a distance: for short plants - 15-20 cm, for medium plants - 25-30 cm, for tall plants 35-40 cm.

Landing of cosmos is carried out by transshipment method . That is, you need to carefully remove the plant from the pot along with the earthy clod (it cannot be destroyed). And transfer the seedling to the hole, fill the voids with earth, slightly compact and water generously.

The plant tolerates transplanting very well, so you don't have to worry about young seedlings. However, at first, more thorough care will be required, but later on you can practically not think about an unpretentious drought-resistant plant. The first few weeks after planting, you need to regularly water the plants, maintaining moderate soil moisture. Subsequently, watering is carried out in extreme heat. Tall cosmos are best tied to a support, especially in windy areas. Top dressing is not necessary, only top dressing at the budding stage with mineral potassium-phosphorus fertilizers is allowed. Also, if you want to get a more lush and long flowering, you should regularly remove faded inflorescences. nine0003

Growing cosmea from seeds. When to plant? At home — Botanichka

Charming Moscow chamomile, kosmos, or kosmeya is one of the flyers, without which no garden can be imagined. Weightless and openwork, delicate, with a calico pattern of pretty flowers against the background of a solid pillow of narrow leaves, kosmeya fascinates with its cheerful character and simplicity. Growing cosmea from seeds is easy even for beginner gardeners. After all, it does not even have to be sown for seedlings. nine0003 Cosmos bipinnatus. © Chloris

Contents:

The most popular double-pinnate cosmea and its hybrids are upright, large, densely bushy annuals from 80 cm to almost one and a half meters high. The leaves are needle-shaped, somewhat reminiscent of dill or fennel, creating a translucent elegant green mass. Against the background of bright greenery, weightless flowers flutter on tall and thin pedicels - basket inflorescences with a beautiful circle of wide reed flowers around a neat yellow center. The petals are very delicate and translucent. The color scheme of cosmea includes all possible shades of white-pink-red palette, sometimes in two-tone variations. nine0003

Despite the fact that today kosmei are represented by numerous varieties that allow you to choose a diverse palette of colors and even plant heights, the ease of propagation of these crops does not change. Without exception, all cosmeas are grown from seeds (both sulfur-yellow, and blood-red, and double-pinnate). Plants give abundant self-seeding, usually if they appear on the site, then forever. But it is not difficult to grow cosmea for the first time. For cosmos, you can use the method of sowing seedlings, although it is much easier to sow the seeds of space directly into the soil, to the place of cultivation. nine0003

When sown in the soil, Moscow chamomile usually begins flowering in July, growing seedlings allows for earlier flowering.

Self-collection of seeds and their selection for sowing

Cosmos seeds ripen perfectly even in the middle lane. Despite the continuing flowering for quite a long time, they can be collected in large quantities on plants on which fading flowers were left already in early autumn.

Cosmea is sold everywhere. When buying, it is enough to follow the general precautions and selection rules. nine0003

Due to the fact that space seeds remain viable for more than three years, one purchase or collection of seeds usually lasts a very long time.

Conditions necessary for growing cosmea

When planting seedlings or sowing in the garden for Moscow chamomile, it is very important to choose the right place. Cosmos are one of the most sun-loving flyers and it will be impossible to admire the weightless beauties in shading.

The soil for cosmea should be fresh, light and loose, nutritious or at least medium nutritious. A high organic content is welcome, as is a sandy structure. Dense or too heavy soils can be easily improved with the addition of compost and sand. nine0003 Shoots of cosmea sown in the ground. © opustopiarium

Sowing kosmeya into the soil

Unlike some other annuals, sowing into the soil for kosmeya is carried out immediately in a permanent place, in greenhouses or seedling beds. But you can choose the timing of sowing at your discretion. Cosmea can be sown in the spring, and use the winter sowing method.

The sowing dates for plants are the same as the standard sowing dates for medium-cold-resistant summers. Cosmees are sown in early May or April, when the risk of persistent night frosts disappears, but without waiting for the complete disappearance of recurrent frosts. Before winter, sowing is carried out when frost begins to bind the soil. nine0003

Cosmea is most often sown not in rows or furrows, but in shallow holes at a distance of 30-40 cm to create an ideal planting density and minimal thinning efforts. 2-4 seeds are laid out in the pits, thinning out the seedlings at the cotyledon stage and leaving only the strongest plants at the optimal distance. When filling large areas with Moscow chamomile, sowing can be carried out in the usual way.

When spring sowing, the soil is strongly moistened beforehand; when sowing in winter, no watering is carried out. nine0003

Cosmea seeds need light to germinate, so they are simply pressed into the soil, fixed in it, but not covered with earth. During winter sowing, places with cosmea seeds are covered with snow. In the soil or greenhouse in the spring shoots appear within 2 weeks.

Growing Cosmos through seedlings

The seedling method is generally only used for rare, new or improved flowering hybrid varieties. This method is inferior in popularity to sowing directly into the ground. nine0003

The soil and containers for sowing cosmea are selected from among the standard ones. Cosmea feels good in a simple purchased substrate for seedlings or self-composed loose and light earth mixtures of medium nutritional value. Sowing bowls should be shallow, but the choice of their size depends on personal preference. Cosmos can be sown in small individual cells or pots of 2-3 seeds, you can use large boxes and rare sowing with thinning instead of diving, or you can carry out standard sowing and pick seedlings. It all depends on the desired number of seedlings and the number of seeds. nine0003

Sowing seeds of cosmea for seedlings begins in March and continues until the end of April, adjusting the desired flowering time of the plant.

The technique of sowing kosmeya is very simple:

  1. The containers are filled with the substrate and the soil is gently moistened with a spray gun. The substrate is not compacted.
  2. Seeds are less often scattered on the soil surface or laid out at a distance of 9-10 cm (or in each cell), 2-3 seeds, lightly pressed down or left on the surface. For germination, cosmea needs access to light. From above, the seeds are moistened from a spray bottle. nine0010
  3. Containers are covered with glass or film.

Conditions for germination of cosmea seeds are not quite standard. In the heat, cosmea sprout worse, indicators from 15 to 18 degrees are considered the optimal temperature range. Containers with cosmea crops are exposed to maximum bright lighting.

Growing plants is carried out in the same conditions in which the sown seeds were kept - in cool and bright light.

Seedlings are dived only if they want to keep all the shoots, avoid thinning, and when not growing in separate containers. Seedlings dive after the appearance of a pair of true leaves. If cosmea was sown in large containers, the plants can be thinned out by removing the weakest ones and leaving the seedlings at a distance of 7-10 cm from each other. In individual containers, the weakest shoots are also simply pulled out. nine0003

Care for young kosmeya is standard, it comes down to careful watering, which does not allow drought or waterlogging. If the seedlings are stretched, the tops of the plants are pinched, but it is better to organize additional lighting and prevent the process of deformation of the sprouts, because tweezing negatively affects flowering and delays its onset.

Hardening of seedlings of cosmeas begins as early as possible, taking the seedlings out into the fresh air for at least a few hours a day on fine days.

Landing in a permanent place is carried out only after the threat of night frost has disappeared, in May. The distance when planting seedlings of cosmea is standard - from 10 to 30 cm to obtain a dense array and beautiful textural spots. The plant is not afraid of transplanting. nine0003 Seedlings of cosmos. © Racquel

Caring for Young Cosmos

Cosmos are surprisingly drought-resistant, but at a young age, at the very beginning of growth, it is necessary for the plant to maintain stable soil moisture. At a time when kosmeya increases the vegetative mass and up to the beginning of flowering in drought, it is better to water the plants. During the flowering period, watering is carried out only during severe droughts and in the heat, in order to maintain abundant flowering and stretch the duration of the flowering period as a whole. nine0003

When growing cosmos, top dressing is not at all an obligatory care item. They begin to carry out at the stage of budding, complete mineral fertilizers, repeating several times over the summer. During the vegetative stage, fertilizing can cause green growth at the expense of flowering. Excess nitrogen is especially dangerous for space.

If tall kosmeya was sown or planted in a windy area, as the bushes grow, it is better to take care of the installation of supports and a garter. Thanks to the light greenery, an ordinary peg is enough for the plant. nine0003

As soon as the first flowers appear, you should start to regularly remove fading flowers. Without such a simple procedure, the flowering of Moscow chamomile will be quite short and not so lush. To collect seeds, the largest flowers are left selectively, while the rest are regularly removed.

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