Even though many perennials do well when cut back in fall, remember that some perennials are actually quite attractive throughout the winter months. Why not leave them if you’re not sure and make notes this year of which ones could use a good trimming (cut back to 6 to 8 inches) next fall and which ones you should allow to languish over the winter months because they add to your winter landscape?
Some perennials have seed heads that are equally attractive (Black-eyed Susan, Coneflower, Yarrow) especially once they’re dusted with snow and also provide food to birds who stick around. Also don’t cut back your evergreen perennials nor your alpines. So, if your other perennials are messy in the fall, clean them up but if not, leave them until spring. You’ll be glad you did.