Growing Green: Dividing Perennials
The first day of spring has come and gone. The snow is deep outside my window, but the sun is shining brightly, and the soft drip of melting snow whisper “spring is on the way!” When the frost leaves the ground, the early perennials will begin to grow. Dianthus (Sweet Williams and Pinks), Iris and Oriental Poppies begin to push their way through the soil, eager to greet the new spring. For the gardener, early spring means planning, seed starting and waiting. Early spring is also the ideal time for dividing many perennials!
The three main reasons for dividing perennials are to control the size of the plants, to help rejuvenate them, and to increase their number. Dividing and replanting keeps rapidly spreading perennials under control, rejuvenates old plants; keeping them vigorous and blooming freely, and is an easy and inexpensive way to gain additional plants for your garden. If your plant blooms between early spring and late June, fall division is recommended. If your plant blooms after late June, then early spring division is ideal. Exceptions to this rule are: Peonies (move/divide in fall only), Oriental Poppies (move/divide in August), Bearded Iris (move/divide in July through September) and true Lilies (move/divide in mid to late fall).
To divide your perennials: dig around the plant at the drip line with a sharp garden shovel. Cut at an angle down and under the roots from various points around the outer edge until you can lever the plant out of the hole. Shake or hose off loose soil and remove dead leaves and stems. This will help loosen tangled root balls and make it easier to see what you are doing. Divide the plants into clumps of three to five vigorous shoots each using garden forks to separate the roots or a sharp garden shovel to cut through tenacious root balls. Replenish the soil with compost and organic material, and replant divisions at the same depth they were originally.
Some plants resent being divided and it should be avoided if possible. These include: Butterfly Weed, Euphorbia, Oriental Poppy, Baby’s Breath, Gas Plant, Japanese Anemone, False Indigo, Columbine, Balloon Flower, Bugbane, Clematis, Gentian, Monkshood, Lupine and Russian Sage.
How often should you divide perennials?
Aster, Penstemon, Monarda, Dianthus, Oenothera, Huechera Centaurea, Delphinium, Tiarella, Phlox, Coreopsis and Achillea should be divided every 1-3 years.
Astilbe, Campanula, Gaillardia, Nepeta, Rudbeckia, Hemerocallis, Liatris and Lysimachia should be divided every 3-5 years.
Cranesbill, Goatsbeard, Hosta, Alchemilla, Pulmonaria, Filipendula, Siberian Iris and Oxeye Daisy should bedivided infrequently: every 5-10 years.
For more information about dividing perennials, visit the extension website at www.extension.umn.edu/.
Welcome to spring, and let the fun begin!
Robin Trott is a Horticulture Educator with University of Minnesota Extension.