When can I divide garden phlox?

Garden phlox (Phlox paniculata) can be divided in spring or late summer/early fall.  In spring, dig up the plants just as new growth begins to appear.  Divide each clump into sections with a sharp knife.  Each division should contain at least 2 or 3 shoots and a portion of the root system.  Replant the divisions immediately.  Keep the newly divided perennials well watered through spring and summer.  Late summer/early fall (mid-August through September) is also a suitable time to divide garden phlox.  Dig up the entire plant, divide the clump into sections, and replant immediately.  Plants divided in late summer/early fall should be mulched in late fall.  A 4- to 6-inch-layer of straw, pine needles, or similar material should prevent repeated freezing and thawing of the soil that could heave late summer/early fall planted divisions out of the ground and cause severe damage.  Remove the mulch in early spring.