How often can I divide perennials?
The frequency of division depends on the species of plant. Most fast growing perennials, such as aster, coreopsis, daylily, hosta, and garden phlox, can be divided every 2 to 4 years. Perennials that spread rather slowly, such as Siberian iris and peony, can be divided every 4 to 6 years. Some perennials, like false blue indigo and gas plant, don’t like to be divided and should be left undisturbed in the garden.