Yes, there are several reasons to prune perennials. The process depends on the season and the reason for pruning.

Late winter or early spring

If dead stems and seed heads have been left on over the winter, they should be cut back to the ground, depending on the particular plant, or a couple of inches high before new growth emerges.

Early summer

Pruning perennials in early summer is called “preemptive pruning.” In the U.K. they call it the “Chelsea chop,” as it is usually carried out at the time of the Chelsea Flower Show (late May). The goal of early summer pruning is to create smaller, later-blooming plants.  This procedure is particularly effective on species that bloom later in the season and tend to get floppy. Examples are Campanula lactiflora, Echinacea purpurea, Joe-Pye weed (Eupatorium maculatum), Phlox paniculata, perennial sunflower (Helianthus sp.)  and goldenrod (Solidago spp.). New England asters and sedums are also good candidates for this treatment. Stems should be cut back by up to half their height. In the New York area, early or mid-June is a good time to try this. A variation of this pruning is to trim only a portion of the stems and thus get an extended flowering season.  Preemptive pruning should not be done on Crocosmia, torch lilies or astilbes.

Late fall/early winter

Plants that have stiff stems and attractive seed heads should be left standing through the winter to provide food for birds and add winter interest to the garden. Plants that collapse and flop should be cut down close to the ground.

Note

Deadheading (removing spent flowers and flower heads) can and should be carried out on most perennials. This will prolong the blooming period for a few weeks.

A great source for advice on perennials is The Well-Tended Perennial Garden by Tracy DiSabato-Aust.

More help with perennial basics from our libguides: https://libguides.nybg.org/perennialsthebasics

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service