When do we cut back perennials, and how? It’s a good question, so let’s dive in.
First, what is a perennial? Almost always, when we talk about perennials, we’re talking about herbaceous perennials that die back in winter, reappear in spring, and whose life span is two+ years. The plant structure of a herbaceous perennial dies when the weather turns cold, but its root structure lives through the winter. Of course, trees and shrubs are perennials, but when gardeners talk about fall clean-up and cutting back the perennials, they’re talking about herbaceous perennials, or in layman’s terms, all their pretty flowers, hostas, heucheras, the fluff and stuff.
Examples of herbaceous perennials are peonies, iris, yarrow, columbine, echinacea, and anemones—all those flowers we love and want in our gardens.
Why Are We Cutting Back Perennials?
It’s easier to remove dead plant material now than in spring when new foliage appears, particularly grasses that need cutting back hard in late winter/early spring for new growth to emerge. It’s impossible to remove the dead once the new foilage has started to show, making for an unsightly mess. Your perennials will be prettier next year if they’re cleaned up this year.
Removing the dead plant material helps clean the garden, avoiding fungal issues, diseases, and infestations for next year.
Cutting back perennials reduces overcrowding in the borders by division or thinning, and this rejuvenates plants and allows for better air and sunlight flow. For a how-to on dividing perennials, read here. For a downloadable chart on which perennials to divide and when read here.
Not All Your Perennials Need Cutting Back
Some perennials provide winter interest and winter habitat and sustenance for wildlife. Examples are perennial grasses and perennial flowers with prominent seedheads (echinacea, black-eyed Susans, and Joe Pye Weed). It depends on the gardener’s desire for tidiness, but if you can bear it, or want to consider a broader ecological approach to your garden, don’t cut back all your perennials in fall, wait until early spring before new leaves emerge.
Which ones? Walk through your garden and note perennials with woody stems, large seed heads, and bushy coverage. Those will benefit birds, bees, and pollinators that need food and habitat for the winter. The fading flowers of Agastache, Liatris, asters, and poppies offer winter interest and are loved by hungry birds.
Don’t forget that pollinators need a place to overwinter and plant debris is one place many bees and butterflies find coverage. Helping pollinators is a year-round garden activity, not limited to just our summertime blooms.
Don’t leave diseased plant material hanging around, though. Clean up the perennials you want to stay, and do not put diseased plant material into your compost bin. Instead, throw it away.
How Far Do You Cut Back And When?
As perennial leaves fade, remove yellowing leaves and any infested leaves. After hard frosts, perennials are dormant, and removing all spent material is acceptable. This can be done in the fall or early spring before new growth emerges.
When cutting back, you are cutting back to the ground. For first-time gardeners, this can be scary, fearing that you’re killing the plant, and you are not. Next spring, it will reemerge and thrive.
Written by Cinthia Milner, landscape consultant, and blog writer.
B. B. Barns serves all Western North Carolina, upstate South Carolina, and Tennessee.