Perennials are commonly divided for three reasons: to control size, to rejuvenate plants, and to propagate a prized perennial. Vigorous perennials may grow so rapidly that they crowd out neighboring plants in the flower bed. Other perennials decline in vigor if not divided at the appropriate time. One of the easiest ways to propagate a prized perennial is to divide the plant into two or more smaller plants.
The best time to divide perennials varies with the different plant species. Early spring (just as new growth begins to appear) is the best time to divide aster, chrysanthemum, hosta, bee balm, sedum, yarrow, obedient plant, perennial salvia, purple coneflower, and ornamental grasses. Other perennials that can be divided in spring include coreopsis, daylily, garden phlox, speedwell, and hardy zinnia.
In early spring, dig up the perennials just as new growth begins to appear. Divide each plant clump into sections with a sharp knife. Each division should contain several shoots and a portion of the root system. Replant the divisions immediately. Keep the newly divided perennials well-watered through spring and summer. Most newly divided perennials do not bloom well until their second growing season.
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