As the gardening season comes to an end, the most commonly asked question I receive is when to cut back perennial plants.

Most perennials can be cut back in either spring or fall with not difference in next year's performance. If time permits you can get a jump on your spring chores by slipping and removing the dead foliage of many of your perennials in fall. But if you have been really busy this fall, don't fret, you can complete your cleanup any time before the spring growth emerges. here are a few tips that may help you decide the best time for you.

In fall you should wait until most of the foliage has turned brown before cutting it back. Since most perennals return from their roots, you may cut the foliage down to ground level.

A good rule of thumb I like to recommend is that if the plant has become unattractive or unsightly cut it back especially if the plant is in a highly visible.

There are several advantages you may encounter if you wait until spring.

Often the foliage has become less attached to the roots, is easier to remove and may not require pruning shears or any tools. Also leaving the foliage or some of the stem will aid you in remembering what is planted where. This especailly helpful for late emerging perennials such as Perennial Hibiscus, Butterfly Weed (Asclepia) and Helenium which often do not peak out of the soil until mid or late May while some other perennials may have already completed blooming.

Some perennials can be attractive in the winter, offering subtle diversion in an otherwise drab landscape. Most ornamental grasses provide great winter interest. 

And some plants provide seed and shelter for birds especially coneflower (Echinacea), Perennial Sunflowers (Helianthus) and Black-Eyed Susans (Rudbeckias).

There are a few noteworthy exceptions that you should not cut back in fall. Some perennials that are on the edge of their hardiness (i.e. are only hardy to your zone and will not survive winters further north or harsh winters in your area) overwinter best if they are not cut back. The 'perennial' Verbenas (such as 'Homestead Purple') is a good example of a plant that has a better chance of surviving the winter if the foliage is left on. The remaining foliage will collect leaves and act as a winter mulch, protecting the plant over the winter. I also recommend that you do not cut back fall garden mems, especially those planted this season. When spring comes and new growth is beginning to emerge, promptly remove the dead stems.

Most woody perennials (often called subshrubs) will survive the winter best if left standing. These include Russian Sage (Perovskia), Blue Mist Shrub (Caryopteris), and Gaura. Once again, when spring comes and new growth begins to emerge, cut back the woody structures down to new growth.
Never cut back lavender in the fall. If you see new growth coming from the base of the plant in the spring, you can cut back to the new growth. Old woody plants oftne will not regenerate new growth at the base of the plant and may not survive a hard spring pruning.