‘Candy Stripe’ cosmos flower. Photo by: Janet Loughrey

Cosmos is a flowering warm-season annual commonly grown from seed. A staple of cottage-style borders, cosmos produce cheerful daisy-like flowers from summer into fall. Even beginner gardeners will enjoy success with this easy to grow flower.

Though individual flowers last just several days, the buds are produced in clusters along the stems for long-lasting color in beds, borders, containers, or cut flower arrangements. Here’s how to grow and use cosmos plants in your yard.

On this page: Basics | Types | Planting | Care | Pictures | Using in the Garden | Frequently Asked Questions

On this page:

Cosmos spp.

Plant type:

Cosmos is a warm season annual that is grown from seed or starts. Chocolate cosmos is a tender perennial grown from tubers or seed.

Zone:

Most cosmos are annual in all zones. Chocolate cosmos is a tender perennial hardy in USDA zones 7-11.

Exposure:

Full sun

Bloom time:

Summer until frost

Growth habit:

Upright or mounding branching habit

Height/spread:

1 to 5 feet tall, 1 to 3 feet wide

Foliage:

Green foliage can be ferny, deeply dissected, or lance-shaped, depending on the species.

Flowers:

Daisy-like flowers 2 to 5 inches wide have single, double, semi-double, or fluted petals encircling a yellow or brown center. The blooms occur in colors of white, pink, magenta, burgundy, yellow, orange, apricot, or chocolate, with some bicolored or multi-colored. Petals can be rounded, ruffled, or fringed.

Benefits and other attributes:

Cosmos flowers are attractive to butterflies and other insect pollinators, while the seed heads are a food source for songbirds and other wildlife. Cosmos may reseed themselves in the next growing season, though some hybrids may not come true from seed.

Are cosmos plants poisonous?

Cosmos are not toxic to pets or children, though the ingestion of any ornamental plant may cause mild discomfort.

Are cosmos plants deer resistant?

Cosmos are resistant to deer browse, though it’s possible to incur some damage if other food sources are scarce.

Photo by Dean Clarke / Shutterstock.

Cosmos can be planted from seed, tubers, or nursery-grown starts. A much broader selection of garden cosmos is available when growing plants from seed.

Where to plant:

Plant cosmos in a site with average well-draining soil that receives at least 6 to 8 hours of full sun.

When to plant:

Sow seeds indoors 4 to 6 weeks before your last average frost date. Direct sow seeds outdoors when all danger of frost has passed.

Soil:

Cosmos are tolerant of a range of soil conditions, but will perform best in average soil with good drainage and a pH of 6.0 to 8.0. Avoid planting in rich soil, which can cause plants to become leggy or fall over.

How to plant:

Cosmos are drought tolerant once established. Water once a week or more often during heat spells. For containers, water when the top 2 inches of soil feels dry. Avoid over-watering and overhead watering, which can lead to fungal disease or other problems.

Amendments and fertilizer:

Cosmos need little or no supplemental fertilizer. Soil that is too high in nutrients can cause plants to produce more foliage at the expense of flowers.

Pruning and deadheading:

Young plants can be pinched to encourage more branching, which will result in a bushier habit and more blooms. Wait until seedlings are 8 to 12 inches tall and snip the top several inches of the main stem to just above a set of leaves. Deadhead spent cosmos flowers regularly to encourage more blooms. After most of the flowers have faded, cosmos plants can be sheared back by up to a third of their size to stimulate new growth and flowers.

Support:

Taller plants may need staking or other support so they don’t fall over.

Pests:

When given the right growing conditions, cosmos are resistant to most pests and diseases. Pests can include aphids, Japanese beetles, leafhoppers, spider mites and thrips. Young seedlings may be prone to slug or snail damage.

Diseases:

Diseases, which are mostly due to overwatering or poor air circulation, can include aster yellows, bacterial wilt, botrytis, curly top virus, fusarium wilt, powdery mildew, and white smut.

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Photo by: guentemanaus / Shutterstock

Chocolate CosmosCosmos astrosanguineus

Habit:

Upright branching habit

Height/Spread:

2 to 3 feet tall, 1 to 2 feet wide

Unlike other cosmos species, chocolate cosmos is a tender perennial grown from tubers. The unusual flowers are a rich velvety reddish-brown with a chocolaty fragrance, hence the name. Add a sophisticated look to containers, beds, or use as a unique focal point. In recent years, new strains have been developed that can be grown from seed. Varieties include ‘Choca Mocha’ and ‘Black Magic Chocolate’.

Photo by: Janet Loughrey

‘Apricot Lemonade’Cosmos bipinnatus

Compact branching habit

20 to 30 inches tall, 12 to 18 inches wide

Uniquely colored petals are soft apricot-yellow with lavender undersides. A mauve-pink ring encircles the bright yellow center for a striking effect. Plant this smaller variety in a cottage-style border or butterfly garden.

‘Candy Stripe’Cosmos bipinnatus

3 to 5 feet tall, 1 to 2 feet wide

Large single flowers 3 to 4 inches wide have a yellow center encircled by white petals edged or striped with carmine-pink. The bicolored flowers, which are variable, create a striking effect in beds and borders. Use this taller variety towards the middle of a mixed border or naturalize in a meadow garden.

Photo by: Walter Erhardt / Shutterstock

‘Purity’Cosmos bipinnatus

3 to 4 feet tall, 1 to 2 feet wide

This classic variety has large pure white flowers 4 to 6 inches across that are produced on tall stems. Makes a superb cut flower. Plant in a cutting garden or cottage-style border. Plants may benefit from staking.

‘Rubenza’Cosmos bipinnatus

Compact spreading habit

24 to 42 inches tall, 24 inches wide

This unusual variety has showy flowers 3 inches across that open to deep ruby-red, shifting to shades of dusky rose and terra-cotta as the blooms age for a multi-hued effect. This compact bushy annual can be used to fill in gaps in a mixed border or to edge a cottage-style plot.

‘Sea Shells’Cosmos bipinnatus

Unique tubular petals resemble sea shells, hence the name. Flowers occur in colors of crimson, pink, or white. Mass in a border or cutting garden for a stunning effect in the landscape. This taller variety will benefit from staking to keep plants from falling over.

‘Sensation’Cosmos bipinnatus

One of the most commonly grown cosmos, ‘Sensation’ is an award-winning variety with flowers 3 to 4 inches across in shades of pink, magenta, and white. Plant this taller cosmos at the back of a cottage-style border or naturalize alongside other easy-to-sow annuals.

‘Bright Lights’Cosmos sulphureus

Open branching habit

2 to 3 feet tall, 1 to 3 feet wide

Semi-double flowers come in vibrant hues of yellow, orange, and red. Mass this shorter species in a curbside strip or cottage-style border. Also known as Klondike cosmos, varieties include ‘Bright Lights’, ‘Cosmic’ series, and ‘Diablo’.

‘Xanthos’Cosmos bipinnatus

20 to 26 inches tall, 12 to 18 inches wide

Ruffled petals are pale yellow with a creamy white ring, creating a subdued pastel effect in the landscape. Pair with lavender or pastel blue flowers for complementary contrast. This shorter variety can be used to edge borders and pathways or planted in containers.

‘Xsenia’Cosmos bipinnatus

18 to 24 inches tall, 18 inches wide

The unusual coloring of ‘Xsenia’ flowers can be variable depending on the light, with tropical hues of pink, peach, rose, apricot, and coral. Use this dwarf variety to edge borders or pathways, or combine in containers with other warm-season annuals.