Pruning Perennials

By Holly Ennist Stewart–

With autumn breezes blowing the leaves off the trees and frost about to settle on the pumpkins, it’s time to start thinking about cleaning up the perennial beds. This is more complicated than it sounds, however, because pruning plants at the end of the growing season is not a one-size-fits-all task. When and how it is done matters a great deal, with different requirements even within the same family, as is the case with roses and hydrangeas. 

It should be stressed that neatness in the garden is a human priority; the majority of plants and the animals they provide food and shelter for benefit more when things are left unkempt in the pre-winter months. Insects hide under leaves. Birds eat seeds and gather materials for nest-making. Plants create seed pods and spread late in autumn, so don’t rush them. Pruning should be postponed until plants show signs of going into dormancy, when their leaves wither and the blooms have dried entirely. For most perennials, this occurs after several hard frosts. 

Every perennial doesn’t need to be cut back at once. Autumn is three months long, after all. Initially, the gardener may want to concentrate on removing foliage from diseased or pest-infested plants to ensure a fresh start next growing season. For example, blight spores can survive on leaves through winter, causing further problems for the host plant in spring. In addition to thwarting disease and controlling pests, cutting perennials back at the right time allows plants to concentrate energy on root systems instead of foliage.

In order to prevent the transfer of pests and disease between plants, use clean, sharp tools when pruning. Wipe the blades with disinfectant or rubbing alcohol between cuts so you don’t spread issues around. Faded flower stems can be cut 6 to 8 inches above ground. As a general rule, cut the rest of the plant down to just above the root crown, about two inches above the soil. On plants with new basal growth (a common sight on early bloomers), prune to just above where it ends. Make the cut at an angle to prevent water from pooling in the stems, which may cause rot or fungus. Dispose of diseased material by burning it or throwing it in the garbage. Other material can be composted. 

Some plants should be pruned later than others because the seeds, plumes, and foliage provide food or shelter for wildlife and beneficial insects. This list includes coneflowers, rudbeckias, and ornamental grasses. Most roses should be lightly pruned in fall, just to eliminate dead or damaged canes. Late winter is the best time to do heavy pruning on roses, right before the new growth season. Lavender also prefers only a light pruning in fall.

Perennials that favor a good fall trimming include peony, catmint, daylily, yarrow, hosta, salvia, hollyhock, and bee balm. By contrast, daisy, sunflower, aster, and Russian sage do better when cut back in early spring. Some perennials, such as hellebore, sedum, and coral bells, prefer to have the old foliage remain atop the roots through winter to protect them.

If you’re uncertain when or how to prune a particular plant, consult a couple of trusted websites or reference books that are in agreement for guidance. If you prefer, stop in or call us with your questions – (973) 838-0174. We love to talk about plants and their care!

 Holly Ennist Stewart is a lifelong North Jersey resident. In 2017, she left a decades-long career in the newspaper industry to work with plants and people who love them. She’s been on staff at Glenwild since 2021.