Cosmos are enormously gratifying everblooming warm season annuals that require minimal care and shine in the garden all summer. The two key garden species are common cosmos (Cosmos bipinnatus), which is very tall and has flowers in shades of ruby red, pink, and white, and sulphur cosmos (Cosmos sulphureus), a somewhat shorter species with blooms in shades of orange-red, orange or yellow. Both are Mexican in origin and quite heat and drought tolerant but they grow very differently.


Cosmos 'Sonata Pink', 'Sonata Carmine' and 'Sonata White' mingle together in a sunny cutting garden. Those flowers browning along the petal edges should be removed to encourage more new flower buds to develop.

The favored species is common cosmos because it blooms for longer and there are more exciting cultivars to choose from. My personal favorites are the dwarf cultivars in the Sonata Series. The bushy, 2 foot plants have the delicate ferny foliage of common cosmos and extra large flowers. Colors include 'Sonata Carmine', 'Sonata Pink' and 'Sonata White.' The 2010 Renee's introduction, 'Rose Bon Bon ', is a new one I'll be trying this year. The medium tall plants reach 3 to 4 feet and become covered with large, fully double, rose-pink flowers with frilly edges. Pretty!


The large, velvety flowers of 'Sonata Carmine' are super vibrant.

For best garden performance, common cosmos needs full sun and well-drained soil with average fertility. Once established, the plants can take some drought but always look better if watered during dry spells. Happy, well cared for plants will often continue to bloom up until frost with light deadheading. Taller cultivars should be staked or they'll topple over. Common cosmos tend to self-sow, so once you plant them they'll come back as seedlings each year.

Sulphur cosmos is a completely different border beast but equally garden-worthy. Most garden-grown varieties are between 2 and 3 feet high. The plants are very fast-growing and can begin to bloom as early as six to eight weeks after germination. When flowering, they put forth a colorful show that typically lasts a few weeks. Deadheading can extend flowering, but not for long. Once these annuals set seed, they begin to turn brown and die.


The golden orange flowers of sulphur cosmos shine in the heat of high summer.

The plus side is that two summer plantings of sulphur cosmos will give gardeners continuous summer blooms. This is an easy plant to sow outdoors from seed. It germinates right away when growing conditions are warm during the day. Just work up the soil in an area, sprinkle with fertile potting mix and keep moist (not wet!). Within a week or so the plants will sprout and begin growing. Once they have begun to bloom, sprinkle more seeds in at the base of the plants and let them germinate. Once the first bloomers start to fade, pull them to give the seedlings below sunlight to grow to their fullest. It's that easy!

The colorful dwarf cultivars in the Cosmic Series are very vigorous and easy to grow. They only reach around 18 inches and come in three cheerful colors, 'Cosmic Orange', 'Cosmic Red' and 'Cosmic Yellow.' The most exceptional of these is 'Cosmic Orange', which was honored with a prestigious All America Selections award in 2000.

Most cosmos have an informal appeal and are well-suited to wildflower plantings and well as children's, butterfly and cutting gardens. These bee magnets also add color and fun to vegetable gardens.  The flowers have a good vase life and look beautiful in a mixed summer arrangements with other free-flowering bloomers, like Queen Anne's lace and tall zinnias.


The ferny, white-flowered cosmos in the foreground blend nicely with 'Lacinato' kale and 'Indian Summer' black-eyed Susans.