So Cosmos are from the Americas?
Yes, the United States Department of Agriculture and the Germplasm Resources Information Network (USDA and GRIN) confirm that although Cosmos has pretty well naturalized to all tropical areas of the world, it is native only to the Americas. As scruffy perennials, there are dozens of species in the Americas (North, Central and South), ranging from as far north as Colorado and Utah to as far south as Paraguay (for people like me, not strong on geography, I will tell you that Paraguay is about midway from the Panama Canal to the tip of South America). So it is a HOT weather plant.
There are at least four different species of Cosmos which are easy-care hot weather garden annuals. The two species most often cultivated in American gardens began as Cosmos bipinnatus and C. sulphureus. There is a third, less common, American variety: 'Southwestern Cosmos' or C. parviflorus, which the Lady Bird Johnson Wildflower Center indicates is native to Texas and other areas of the southwest. 'Wild Cosmos', or C. caudatus, is eaten as a salad or vegetable in Indonesia and Southeast Asia and is believed by people there to have beneficial effects on health. There are certainly generations of people all over the world who believe Cosmos ssp. has always flowered in their landscape. DNA evidence leads scientists to agree that Cosmos originated in the Americas. (Similarly, neither I, my mother nor her mother can remember a North America without Queen Anne's Lace or Dandelions--both introduced from Europe.) Still, all indications are that even C. caudatus is also native to the Western Hemisphere. However, for the purposes of this article, we will focus on C. bipinnatus, sometimes labeled Mexican asters, and on C. sulphureus, also called Orange Cosmos or Klondike Cosmos.
C. sulphureus or C. bipinnatus?
Sulfur is the Greek term for yellow, and C. sulphureus, as you may have guessed, tend to be yellow or orange. C. bipinnatus, on the other hand, are the pale pink, dark pink or white ones with fine, ferny or thread-like foliage. As with so many annuals, though, once European breeders got their hands on Cosmos, the cheerful daisy-shaped flowers became available in different forms and colors, different heights, and even blooming sooner or later in the summer.
cultivation: in general
Cosmos are definitely one of those flowers you've heard about that do best in poor soil. Fertilizer may make them taller or greener, but it will not make them make floriferous. Although most cultivars are drought-tolerant once established, Cosmos appreciate supplemental water, and should reward you with more or bigger flowers. Grow them in full sun if you have it. The taller varieties may prefer to be planted closely together so they can lean on each other for support; the taller Cosmos varieties do not have deep enough roots to enable them to stand up to high winds, and if it gets windy, you may find yourself wishing you had staked them.
According to some sources, Cosmos' flowering time is determined not by time of year, but by day length. They usually only flower after the summer solstice, when the days begin to get shorter. Therefore, starting them inside or planting them very early will result in taller plants which don't flower any sooner. Some cultivars have been bred which are not dependent on day length; these may work better for earlier blooming.
Cosmos are a must for bird or butterfly gardens. As is true of other flower colors, the ones described as "red" really look like a very deep pink to me. They are deep rose, darkest magenta, or maybe ruby red, rather than scarlet, carmine or vermillion. Thus mixtures labeled "white, pink and red" look like beautifully harmonious shades of white, pale pinks and darker pinks to me, but peonies are also said to have no really true reds, only intensely deep pinks, and we don't complain. Cosmos flower petals radiate out from bright yellow centers which are irresistable to bees, butterflies and birds.
C. bipinnatus varieties
Look for the 'Double Click' series which has multi-petalled flowers (almost like carnations), or the 'Seashell' types, described as 'quilled' or 'rolled' (although I might call them 'cactus-flowered' and I don't see the resemblence to seashells). Then there are height variations, from 'Sonata' (pinks) at around 24" to 'Sensation Mix', another reliable "pink, white and red" variety with tall, sturdy stems, but definitely later blooming. 'Psyche' mix is another cultivar with sort of extra petals in the middle. (It's described as "double-flowered" but that distinction really belongs to the 'Double Click" series.)
As time goes on, breeders are sorting out the colors and the double-flowering ones. 'Daydream Mix' and 'Picotee' play with the white to pink ratio; 'Picotee', as might be expected, has a narrow dark pink border along a white petal while 'Daydream Mix' has pale pink petals which darken toward the middle. These are only some of the more common cultivars you may run across.COSMOS SEASHELLS MIX
and C. sulphureous
There are varieties of C. sulphurureous, too, from orange, true red and yellow mixes of various heights through to separate colors from the mixes. Try 'Cosmic', it's dwarf, at 12" high, and is available in yellow, orange, or a true red, or more commonly, as a mix; 'Bright Lights' is an orange and yellow mix that grows to 40" tall at least. C. 'Tetra', C. 'Raphael' or C. 'Ladybird' (which comes in orange, yellow or lemon and is, again, shorter) are also out there and available. I think the richer reds and browns of the new sulphureous cultivars are quite elegant, but I may be thinking of something different, like a rich red or brown winter coat, and not an annual flower bed.
All Cosmos cultivars feature a bright yellow eye, which birds, butterflies and bees seem to adore.
Although Cosmos plants do not tolerate frost, the seeds don't seem to mind it. Cosmos naturalizes well, as I said above, and often re-seeds itself even in temperate climates. This tells us that Cosmos is a perfect candidate for direct-seeding in the fall or spring and ideal for using with the Winter Sowing method; in fact, that's how I sowed my first Cosmos. You really don't need to spend extra money on seedlings in the spring (if you can even find them), since Cosmos are easy to grow in any sunny, hot and even dry location. (One site even said "if you have trouble grrowing Comos, take up golf!") They germinate quickly and bloom fast. Cosmos are often included in "wildflower" mixes or "meadow" mixtures.
grow a meadowfull yourself!
I ran across a few places which sell Cosmos seed by the ounce! You could fill a field with sunny yellow and oranges, or produce a pile of pale pinks. Read this Dave's Garden article (from 2008) about seeding a meadow first for tips, buy an ounce or two of Cosmos seed, and convert your blank spaces into cosmos patches! .
keep them dead-headed or picked
In order to insure a continuing supply of delightful flowers, continue deadheading Cosmos all summer. Or, you may pick them for use in a vase indoors. They should last 7-10 days in a vase and the ferny foliage really helps a cut bouquet look airy and ethereal. (Some suggest planting successive crops for continuous flowering, but that is really not necessary!)
cut them down
If your Cosmos seem to stop floweriing (or lessen their flower prouction) after a good first start, cut them back by two-thirds, leaving at least a foot (12") of stem and foliage. They should bounce right back with more flowers than ever.
a few specifics
Click on the following links for differing opinions about whether to fertilize or not, whether to water or not, and descriptions of various cultivars.
BURPEE.COM an article about Cosmos history and cultivation according to Burpee Seed Company, and of course, they sell the seeds.
ANNIE'S ANNUALS if you live in California or don't mind paying for shipping, you can buy plants here. Better to just steal her information.
WILDSEED FARMS has 14 varieties of Cosmos seeds.
THOMPSON AND MORGAN has 24 varieties!
OLD FARMER'S ALMANAC has some more information
TEXAS A & M thinks Cosmos are the best annual for Texas, but you'll have to copy and paste this link:
Pictures: thanks to Dave's Garden members and subscribers Dinu, Evert, kell, kwanjin, muibien, Songbird839, and Wikimedia Creative Commons contributor KENBEI.