In light of 2016’s many significant events, you may not have noticed that it was the “Year of the Cosmos”. But noticed or unnoticed, Fleuroselect, the Netherlands-based horticulture trade group, decreed that last year, cosmos were the brightest stars in the horticultural heavens.
It may be a coincidence, or not, but at the same time, Britain’s Royal Horticultural Society undertook a massive trial of cosmos varieties at its botanical garden at Wisley. Photos of the trial beds show scores of tidy mounds of brightly colored flowers in a range of heights. The rising tide of cosmos popularity was so significant that noted English garden writer, Graham Rice, wrote it all up in an article for the Telegraph newspaper.
Celebrities pay publicists a fortune to get that kind of press. Cosmos, knowing nothing of reality TV or the going rate for celebrity status, went right on blooming while the international spotlight focused on their colorful petals. Unlike many celebrities, they went viral while keeping their cool.
Gardeners who grow reliable annuals have been wild about cosmos for years. Vita Sackville-West, one of the doyennes of twentieth century garden writing, threw caution to the winds in her garden and grew ‘Orange Ruffles’, which she described as “three-foot tall, feathery of leaf, starry of flower, long lasting, and pretty enough in a mixed bunch to please even Mrs. Constance Spry.”
Though English gardeners love them, cosmos are a New World species, originating in Mexico, Central and South America. Cosmos bipinnatus, an annual and one of the three species with descendants in commerce today, was introduced from Mexico about 1800. Supposedly Spanish priests grew them in the gardens of Mexican missions. The flowers’ daisy-like appearance attests to the species membership in the large and far-flung daisy or Compositae family.
Once cosmos hit the American and European markets in the early decades of the nineteenth century, their popularity grew. Seed vendors offered excellent bipinnatus strains like the aristocratic-sounding ‘Lady Lennox Pink’. But despite their alluring flowers, cosmos were not perfect. Nineteenth century varieties were late bloomers, taking months to go from seed to flower. Even “early-blooming” varieties needed sixty to seventy days to flower. Gardeners in areas with short growing seasons who could not start seeds indoors sometimes found themselves with beautiful plants that only bloomed for a month or so before early autumn frosts set in and killed them.
All of that changed in the 1930’s with the introduction of the ‘Sensation’ strain of cosmos that bloomed in only fifty-six days. The relatively short time from seed to flower meant that more people could enjoy more cosmos for longer periods of time. The ‘Sensation’ strain continues to be available today. Nearly concurrent with the arrival of ‘Sensation’, breeders developed double-flowered cosmos, which extended the available offerings and continue to be popular. More recently—2007 to be exact—another form appeared, this time with petals fused into a shape that made the flowers resemble cupcake papers. Dubbed ‘Cupcakes’, these plants are available in white, pale pink and deep rose.
The bipinnatus strains and varieties are wonderful, but the color range is somewhat limited to white, some pale yellows, like ‘Xanthos’, and a host of pinks. Another species, Cosmos sulphureus, features slightly smaller flowers than the bipinnatus offerings, but those flowers extend the cosmos color range into deep yellows, oranges and dark reds. Native to Mexico, the sulphureus species can grow to a towering six feet, but breeders have remedied that by perfecting more compact varieties. Among the most popular strains is ‘Cosmic’, which grows only 12 to 24 inches and features semi-double petal rows.
Gardeners and chocoholics found a new reason to rejoice in 1870, when Cosmos atrosanguineous were discovered in Mexico. These plants grow from dahlia-like tubers and boast small, red-brown flowers with a chocolate scent. Identified in the wild a second time in 1878, it has never been found again. Fortunately for the survival of these chocolate-scented beauties, the atrosanguineous species proved popular as a garden plant. A recent variety, ‘Choco Mocha’ is perfect for container growing, rising only 10-12 inches. Though the chocolate cosmos are perennial, they are tender in cold winter areas and should be treated like annuals. It is possible that digging and storing the tubers, like the standard over-wintering treatment for dahlias, might perpetuate choice plants over the winter. Doing so would make an excellent plant experiment for gardeners who are so inclined.
Another English gardening deity, Gertrude Jekyll, liked to use cosmos with asters for end-of-season color. This would work especially well with the white, pink and rose bipinnatus types, whose colors echo the predominant aster hues.
My longtime favorite cosmos is ‘Purity’, a bipinnatus variety that has been around for over eighty years. It features radiant white petals, ferny light green foliage and a floriferous disposition. Working well in a rose or mixed annual/perennial/shrub border, ‘Purity’ rises to three feet tall. If you deadhead or pick the blooms regularly, the plants will exert themselves from late spring or early summer until fall. If you are a haphazard planter, clumps of ‘Purity’ make excellent buffers between potentially clashing color combinations. The cut stems also last very well in arrangements. What more could anyone want?
As with many annuals, cosmos grow best in well-drained, consistently moist soil. Site the plants in a sunny spot for the maximum number of blooms. Sometimes happy cosmos will self seed. If you want to encourage this, stop picking or deadheading at the end of summer or the beginning of fall, depending on when first frosts usually hit. The following spring, watch for seedlings, being careful not to disturb them as you haul out the onion grass and chickweed. Mine tend to self seed on occasion, but I always buy fresh seed to augment supplies.
The root word that gave rise to the common name, “cosmos”, also gave us the words “cosmic”, “cosmology” and, of course, “cosmos”, signifying the universe. In the small universe of my garden, flowering cosmos shine brightly every year.