Is there a perfect perennial? And what would we mean by a “perfect perennial” for our ornamental gardens?
Well, first of all, it would be trouble free. Its blossoms would of course be beautiful, it would flower profusely and for a long time during the growing season. And if you cut its flowers and put them in a vase in the house, they would last and last.
Is there a perennial like this?
Look no further than Stokesia laevis ‘Blue Danube’, which many plant experts think is indeed the perfect perennial. I sure do. Its common name is Stokes’s aster, for the late 18th and early 19th century botanist and physician Dr. Jonathan Stokes, who developed the use of foxglove extract (digitalis) to regulate heart rhythm, but who also found the light blue-violet daisies of this aster-family species growing wild from South Carolina to Florida and west to Louisiana. ‘Blue Danube’ is a later cultivar dressed in lavender blue.
“Trouble free” is an understatement. It’s not bothered by mildews or diseases. Insects avoid it. Rabbits and deer won’t eat it—although gophers, those indiscriminate little subterranean bandits, might chew the roots. Because it’s native to the Southeast, it sails through droughts and furnace-hot weather. It likes full sun, but it doesn’t like wet feet in winter, so plant it in well-drained, loose, sandy soil.
Its only drawbacks are its lack of scent and its tendency to fall over in the strong winds of fierce thunderstorms. A little support, such as a stick or two inserted in the soil, can help keep the stems upright. In regions with cold winters, like USDA Zones 4 and 5, it will benefit from a layer of mulch thick enough to protect it from below zero temperatures.
It starts blooming in late June or July and continues in most of the country until hard freezes knock it back. In warm climates, such as we have here in Sonoma County, it will continue blooming sparsely through the winter if you regularly deadhead the spent blooms.
And what blooms! ‘Blue Danube’ flowers are uniquely beautiful. Each is three or four inches across, ranging in color from lavender blue to blue-violet with whitish centers, and their shape seems devised by a master jeweler. An inner set of slender, threadlike petals forms a circle that is topped with a dazzle of white stamens emerging from the center, giving the inner part of the flower a glittery appearance. This disk is surrounded by much longer petals that are deeply divided into four or five lobes at their tips, making a filigreed backdrop for the dazzling center part of each flower.
Rains will bring it through all but the most desperate droughts. The long summer drought in a Mediterranean climate such as California is a bit much for this plant, but a few deep waterings during the dry months will see it through until rain returns. It tolerates filtered sunlight, but it prefers full sun. Deadheading greatly increases flowering. Nick off individual spent flowers. If a flowering stem seems to have given its all, cut it back to the lance-like foliage at the base of the plant and it will send up a fresh stem.
To get a sense of its requirements, know that it is at home in the sandy wetlands, bottomlands, wet pine woods, savannas and ditches along the southeastern Atlantic coastal plain. In that climate its leaves persist all winter, so it’s an evergreen perennial that typically grows from 12 to 18 inches tall.
In gardens, place it in the front of the border or bed, so you and visitors can admire its beauty. In landscapes, find well-drained areas along ponds, streams or water gardens, but not where winter moisture will pool at its roots, or they’ll rot and kill the plants. Plant ‘Blue Danube’ in small groups of three to five plants, or mass a dozen or more as though they had been growing there since time immemorial.
If you do make a mass planting of young potted starts, you’ll most likely want to give them a natural appearance rather than place them in neat rows and files. A good way to do this is to gather as many markers as you have plants. These can be anything that you’ll be able to easily recognize after you scatter them, such as marbles, or nickels, or filberts—whatever.
Take a handful and with a wide, sweeping motion, scatter them across the soil where you want the perennials to grow. If you still have more, scatter them the same way a little farther on. And then plant each seedling of the perennial where a marker has landed.
Along with all its other virtues, Stokes’s aster is easy to divide in spring. Simply cut the root ball into three to five divisions. Even small divisions root readily.
Finally, no plant is an island, entire unto itself, and so pair this beauty with Scabiosa columbaria ‘Pink Mist’, the pink pincushion flower. It also goes well with the pale yellow of Coreopsis verticillata ‘Moonbeam’ and the lemon yellow of Achillea ‘Moonshine’. Or site it by the pink mist of Gypsophila paniculata ‘Flamingo’.
As you can see, with Stokesia laevis ‘Blue Danube’, you can hardly go wrong.
Image courtesy of Walters Gardens