Plants A to Z

Guides to Grow Cosmos Flower

Cosmos are a low-maintenance annual plant with a profusion of blossoms that may be started in the garden after any fear of frost has passed. Cosmos are easy to grow and provide a profusion of blooms. These typical cottage garden flowers attain full maturity in around two months.

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Cosmos are a low-maintenance annual plant with a profusion of blossoms that may be started in the garden after any fear of frost has passed. Cosmos are easy to grow and provide a profusion of blooms. These typical cottage garden flowers attain full maturity in around two months.

This plant tends to be longer to germinate, but it blooms fast after that and continues to flower through the fall. The flowers sit atop long slender stalks and make a cloud of color that looks appealing throughout the summer and attracts bees, butterflies, and birds to your garden. Cosmos blooms look a lot like daisies.

They come in a diverse range of hues, with more varieties generated every year. The leaves grow opposite on stalks and are highly lobed, pinnate, bipinnate, and feather-looking, depending on the species. If you plan to raise cosmos and live in the southern U.S., consider keeping them as potted plants since they tend to be invasive there.

Cosmos Care

Cosmos grow readily in beds and produce wonderful cut flowers. When established, the plants can tolerate drought, poor soil conditions, and general neglect. They even self-sow. This is a genuinely low-maintenance plant. While some pests, like aphids, flea beetles, and thrips, do appreciate cosmos, they're easy to remove with a powerful spray of water or insecticidal soap. Aster yellows, bacterial wilt, and powdery mildew may also harm the cosmos.

Space plants suitably ensure optimum ventilation to avoid illnesses. The taller kinds look beautiful surrounded by goat's beard, coneflowers, and black-eyed Susans, for example, in the middle or back of the border. Shorter varieties provide wonderfully colorful, airy border plants.


For the best flowering, pick a place that gets full sun. When planted in shady areas, Cosmos will grow in moderate shade but have fewer blooms and be less vigorous. These plants will also grow under unbroken full sun in the warmest temperatures, much like their native habitat: the desert parts of Mexico and Central America.

Soil Cosmos plants prefer somewhat acidic soil; however, they flourish in poor soil where many flowering plants droop. Cosmos perform best in medium moisture, well-drained soils, but they will perform effectively in dry soils. Avoid planting in rich soil; it can lead the plants to get too tall and flop over. You can prevent drooping by anchoring the plants or growing them next to other plants that can support them.


Once established, you will not need to water your cosmos plants unless there is a protracted drought. Where water is restricted, these are the last plants that require irrigation.

Humidity and Temperature

Hot weather is excellent for cosmos, and they grow in any humidity level.


Fertilizing can badly damage cosmos. Cosmos can handle poor soil. Too much fertilizer can typically lead to vigorous plants with loads 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 typically utilised in gardens in landscaping. 

  • Cosmos sulphureus is native to Mexico, Central America, and northern South America. With golden yellow blossoms, it is exceptionally drought tolerant and enjoys warmer weather. The plant can grow from 2 to 6 feet tall and produces flowers that are both double and semi-double in appearance. Some of the more recent varieties tend to be shorter, more orangy, and with smaller flowers.
  • Cosmos bipinnatus are brilliant daisy-like flowers that appear in white, pinks, reds, and orange. They are lesser in stature than C. suphureus, standing between 1 and 4 feet tall, and are available in various popular hybrid series. Although they are not nearly as heat tolerant as C. sulphureus, C. bipinnatus will grow well in just about any sunny location.
  • Chocolate cosmos is a different species: Cosmos atrosanguineus. The dark crimson blossoms smell like chocolate. This perennial is hardy to USDA zone 7; however, it is heavier maintenance than the annual cosmos. Like dahlias, it grows from tubers.

Other common cosmos cultivars include:

  • 'Bright Lights' mix: This cultivar boasts a blend of flamboyant yellows, oranges, and reds.
  • 'Cosmic Orange': This stunning, semi-double orange blossom has remarkable drought tolerance.
  • 'Peppermint Candy': An award-winning cultivar, the petals are splashed in magenta and white.
  • 'Sea Shells' series features unusual tubular petals with a lovely blend of pastel colors.
  • 'Ladybird': This cosmos is a shorter variety that blooms in various colors, including red, yellow, orange, and gold. It grows 12 to 16 inches tall and blooms in a variety of colors.


The maintenance cosmos plants need deadheading which will lengthen the flowering season. If you fall behind, shear the plants by roughly one-third, when most flowers have faded. This method of trimming promotes a second flush of leaves and blossoms. By the end of the season, you can cut off the plants at ground level or pluck them up, roots and all. In contrast, if you leave the plants in place, they may self-seed for the following season.

Propagating Cosmos

Cosmos plants rapidly self-seed. It's better to propagate these plants when the fear of frost is gone. Although spreading seeds is the best and easiest technique to propagate this plant, you may also propagate via stem cutting. When you take stem clippings, it stimulates leaves and bloom growth. Besides the seed, stem cutting is the greatest way to reproduce 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 point, push straight down in the soil approximately 1 to 2 inches deep, producing a shallow hole.
  3. Look for a cosmos sprout that has 3 to 5 leaf nodes on the stem. Cut under the last leaf node. The last leaf node, carefully clip off the leaves, leaving the node intact for new development.
  4. Bury the cut tip of the stem in the pencil-made hole. Check to see that the last leaf node is above the soil line before continuing. Push down the soil around the stem, compacting the material to keep the branch upright and in place.
  5. Water generously and maintain moisture. Within three weeks, you should begin to witness new leaf growth. If you do, you can carefully remove the root ball out of the container, Transplant the root ball to its new place.

How to Grow Cosmos From Seeds

Cosmos are uncomplicated to grow from seeds. Start seeds inside, four to six weeks before the final frost. Or if you can sow cosmos outdoors straight in the garden well after the threat of frost has gone. Cosmos proliferate but can be killed by a late frost, so don't push it. Cosmos germinate in 7 to 21 days at 75 degrees Fahrenheit, followed by flowering in about 50 to 60 days.

Dislodge the soil till it reaches a depth of 8 inches. Plant the seeds and cover them with 1/4 inch of fine dirt. Seed packs usually indicate specific spacing, such as at 2-foot intervals, or you can scatter the seeds and allow the plants to support each other as they grow. You can always thin them out later, transferring the surplus plants to another part of the garden.

Potting and Repotting Cosmos

When growing cosmos in pots, make sure the container includes bottom drainage holes. Cosmos can't withstand incredibly moist, muddy soil. Plant one cosmos plant every gallon of water in your container. If you're growing in a pot, don't enrich the soil because it will cause your plants to grow tall, lanky, and droopy. Tall cultivars will also require support in containers. Plan on using a heavy, 12-inch-diameter container at the very least.

Cosmos Overwintering is a once-a-year plant. They will perish if left outside in freezing conditions. However, if you decide to cut dead flower heads to shed their seeds at the end of the flowering season, cosmos seeds will fall dormant and sprout when the soil warms up again in the spring.

You'll need a bright whole sun-growing lamp for at least 7 hours a day if you have a potted cosmos in a container and want to maintain it alive during the winter. Any blooms that emerge will need to be snipped off as soon as they appear. The life cycle of this plant comes to a close with flowering when it produces seeds for the following season.

How to Make Cosmos Flower

Cosmos plants require direct sunlight to blossom. It may not flower if there is even a sliver of shade. It would help if you also deadheaded the old blossoms to encourage additional blooms to appear. Prune between the main stem and a leaf for faster flowering. The lower the branch is cut, the longer it takes for extra blossoms to grow.

Cosmos Issues that People Have

Cosmos are simple to grow and care for throughout the growing season. In most cases, they are disease and insect-resistant; nonetheless, some pests can be a nuisance and impede their growth.

  • Wilting or Discoloration of the Leaves

There are two possible causes if your plant gets plenty of water and isn't wilting from dehydration. A common fusarium fungal infection can cause wilting and leaf discoloration in plants. Fusarium is most likely present if you pull up the plant and discover a pink mass on the roots.

The entire plant is doomed, will die, and must be destroyed to prevent the fungus from spreading. If the roots are healthy when dug up, the plant may have a bacterial wilt infection. The bacteria causes wilting at the base of the stems. This plant will perish and should be removed from the environment.

  • Leaf Drop and Yellowing Leaves

Powdery mildew is mostly a problem for plants that grow in the shade.

3 Fungus spores float in the air and land on a shaded host plant. It causes yellowing leaves and leaves to fall off by coating them with a powdery white coating. To avoid powdery mildew, give your plants plenty of air, intense light, and water the soil rather than the leaves. If your plant has fungus, use a horticultural fungicide as directed on the label.

  • Flowers that are distorted or stunted in their growth

As an aster, cosmos is susceptible to aster yellows, a disease spread by leafhoppers (a tiny grasshopper-looking insect). The leaves will become mottled with yellow, and the blossoms will become deformed or stunted. Because there is nothing that can be done to help these plants recover, they should be killed.

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Elissa Sanci
Elissa Sanci
Elissa Sanci, the owner of the website, and senior writer of New York Garden; graduated from Santa Barbara City College – a famous public school in California with many diverse training professions, and she majored in horticulture.