Topping or cutting back herbaceous perennials this fall can help prevent the overwintering of diseases and insects, although leaving some material can help to hold a snow cover during the winter.
Mulching in the fall will help to prevent plants from being forced from the ground, but it should be done after the ground is frozen. Watering lightly after applying the mulch will help hold it in place.
To prevent root damage during the winter, it’s important to have a reserve of moisture in the root zone for all plants in the yard. Fill the soil profile with water in mid-October or just before the ground freezes.