Cosmos are native to Mexico, but their name actually comes from the Greek word "kosmos," meaning "beautiful thing." And what beautiful things they are: The vivid annuals flourish in beds, borders, containers and cutting gardens, yielding blooms all summer long.
A longtime favorite of gardeners, cosmos are reliable, affordable (a six-pack of seedlings will likely set you back $1.50; a seed packet, even less), easy to grow, and adaptable to most parts of North America.
Cosmos have been a staple in American gardens since the 1930s, when the first cultivars were bred. Whether you've been long acquainted with them or are planting them for the first time, you're certain to be charmed by these brilliant summer flowers.
Cosmo species
The most commonly grown Cosmos are from one of two species: Lace cosmos (Cosmos bipinnatus) are yellow-centered flowers that range in color from white to pale pink to reddish or purplish pink (the one called 'Yellow Garden' is the notable exception color-wise); sulphur cosmos (C. sulphureus) have blooms that span the sunny spectrum from bright yellow to blazing orange to near red.
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Besides color, the other obvious differences are in the species' flower sizes and foliage. Lace cosmos have blooms that are about 3 inches wide and ferny foliage with a delicate texture. Sulphur blossoms are a bit smaller but have more rows of petals. Their leaves resemble those of marigolds.
There is also a third species, chocolate cosmos (C. atrosanguineus), with dark-maroon flowers that have a cocoa-like scent. In favorable climates (USDA Zones 7 to 10), they behave like perennials, appreciating a deep mulch in winter toward the colder end of their hardiness range.
Elsewhere, starting in late fall, the tubers of chocolate cosmos need to be stored in barely moist peat in a protected spot.
Cosmos glossary
Regardless of the variety you choose, always read the label before planting to see how tall the cosmos will grow. Heights vary widely, between 14 inches and 5 feet, and you don't want to end up with a very tall flower if you were expecting something more petite.
Look for these favorites at your garden center or nursery:
-- Cosmos bipinnatus 'Sea Shells': This hybrid blooms in a range of colors, including pink, carmine red and white. Its individual daisylike flower petals are rolled and have a funnel-shaped appearance. Sea Shells will reach 36 to 48 inches in height.
-- C. sulphureus 'Bright Lights': The early-flowering, semi-double (having more than one row of petals, though fewer overall petals than full doubles) blooms of the series add fiery color to the garden from spring until the first frost. These stocky, weather-resistant cultivars come in bright yellow, gold, orange and scarlet, and are perfect for sunny borders.
Bright Lights typically reach 36 inches in height.
-- C. bipinnatus 'Sensation': The Sensation series cosmos have feathery, bright-green leaves. From early summer through the first frost, they bloom flowers up to 4 inches across.
Selections of the series, including Sensation White and Sensation Pink, are grown for their pure colors. The white fluted petals of Sensation White make it a striking addition to any bed or border. Sensation White and Sensation Pink will reach 24 to 36 inches in height.
-- C. bipinnatus 'Sonata White': Selections of the Sonata series, including Sonata White, are dwarf, or compact, plants. Like all bipinnatus varieties, Sonata White has daisylike flowers and ferny foliage with a fine texture. It will reach 14 to 18 inches in height.
Growing cosmos
Dependable and hardy, annual cosmos don't even require a head start indoors. After temperatures outdoors have stabilized to at least 60 degrees Fahrenheit, sow seeds under a one-eighth-inch covering of soil. (If you prefer to start them indoors, plant them about six weeks before final frost in your area.)
You won't need much fertilizer -- overfertilizing will produce bushy stems and lots of foliage but few blossoms. And don't worry about dry summers because these heat-loving plants will flourish in areas where soil is lean or rainfall sparse.
To keep plants in bloom for many weeks, deadhead spent flowers regularly. If, around midsummer, the flowers on the taller annual cosmos begin to bloom less frequently, cut the whole plant back by about half its height to prompt another display in late summer that will last through fall.
Don't be too quick to pull up withering cosmos at the end of the season.
Birds (particularly gold finches) enjoy snacking on their seedheads in autumn, and the seeds that they miss may fall to the ground, rewarding you with a whole new crop next year.
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