There is no difinitive yes or no answer to this question. Some gardeners prefer to cut back tall stems, shape flowering stalks and shabby foliage in the fall. The seed heads of coneflowers and ornamental grasses are often left to lend attractive winter interest in the garden. The basal growth of perennials should be left untouched. The clean-up can be dependant on the weather; what does not get cut back in the fall is easily done in the late winter or early spring.
For more information, please see the PlantTalk script "Perennials: maintaining."
