August is an excellent time to divide certain tired-looking perennials, including bearded iris, daylilies, hostas, Shasta daisies, garden phlox, Oriental poppies, hardy geraniums, and astilbe. Choose a mild, overcast day, water well afterward, and make sure every new piece has healthy roots and shoots so it can settle before frost.
The telltale signs are a bare center, fewer flowers, flopping stems, or a clump that has simply become too large for its allotted patch of earth. Plants, like dinner-party guests, are much more charming when they are not sitting on top of one another.
