When to divide perennials
is to divide spring-flowering hardy perennials in fall, fall-flowering perennials in spring.
That works fine for the most part, but winter comes early in my New England garden and gives divisions little time to reestablish themselves. So I like to divide perennials in spring. It鈥檚 the season when I may have less time, but when both the plants and I are most energetic.
[PDF] may be on slightly different schedules than we are in Vermont, but North or South, East or West, all divisions require a bit of pampering until their roots can take hold.
One warning accompanies dividing in spring: Some perennials, especially those that bloom in spring or very early summer, may not flower the first season after being divided. I sometimes wait on those plants and divide them after they stop blooming.
Do the plants really need dividing?
Dividing perennials is a drain on my time and energy, so the plant needs rejuvenating, it has outgrown its space, or I want more plants. I know when I鈥檓 up for the job: an overcast day when I can dig, divide, and replant before nightfall.
It鈥檚 equally important to recognize plants鈥� signals that it鈥檚 time to divide. Plants with fewer or small flowers, plants that have lost vigor, plants that flop open at the center, plants with dead centers 鈥� all are signs that a perennial needs to be divided.
Some perennials 鈥� gooseneck loosestrife (Lysimachia clethroides) is a good example 鈥� spread so aggressively that I have to rein them in almost every year. And many vigorous perennials, such as New York asters (Aster novi-belgii), garden phlox (P. paniculata), and sneezeweed (Helenium autumnale), need frequent renewal and control, every three or four years in my garden.
But in my experience, most perennials don鈥檛 need to be divided as often as the experts claim. Garden references, for instance, declare that astilbe (Astilbe x arendsii) and tickseed (Coreopsis grandiflora) need dividing every year or two. My tickseeds need dividing only every five or six years, and I haven鈥檛 touched my astilbes in two decades.
The bottom line is that if plants are healthy, blooming well, and staying in bounds, leave them alone.
Perennials that rarely need dividing
Frankly, I don鈥檛 have time to divide the same plant every two years. If you don鈥檛 either, choose perennials that rarely require division. Hostas (Hosta cvs.), peonies (Paeonia cvs.), and balloon flower (Platycodon grandiflorus) are among the perennials that can go a decade or longer without being divided or crowding their neighbors.
Even better, some perennials, such as butterfly weed (Asclepias tuberosa), oriental poppies (Papaver orientale), and Russian sage (Perovskai atriplicifolia), are so difficult to divide that it鈥檚 probably foolish to try. A good list of these Do-Not-Divide plants is of Gardens by the Bay in Ontario.
And a second warning: If you divide one of these Do-Not-Divide prima donnas, expect the divisions to sulk for at least a year.
Coming Tuesday: How to divide perennials
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Karan Davis Cutler blogs regularly at Diggin鈥� It. She's a former magazine editor and newspaper columnist and the author of scores of garden articles and more than a dozen books, including 鈥淏urpee - The Complete Flower Gardener鈥� and 鈥淗erb Gardening for Dummies.鈥� She now struggles to garden in the unyieldingly dense clay of Addison County, Vt., on the shore of Lake Champlain, where she is working on a book about gardening to attract birds and other wildlife. To read more by Karan, click here.
