Cutting back. You can cut herbaceous perennials to the ground as soon as tops die back in fall.  Let woody and evergreen perennials stand until spring, then cut plants back by about half to just above swelling buds.

Dividing. To keep flowering well, most perennials need to be divided every few years. You'll know it's time to divide plants when their centers start to die out or when the plants start producing fewer or smaller flowers each year. Divide spring bloomers in fall and summer-to-fall bloomers in early spring. Dig up each clump with a shovel, then tease its roots apart by hand or cut them apart with a knife or spade before replanting.