To Prune, or Not to Prune? The Perennial Question
As the weather cools, many of us are preparing for fall garden cleanup and facing some important existential questions. Chief among these questions is, of course: To prune, or not to prune?
As with most things, there are different approaches to fall care of the perennial garden. Some prefer the tidy appearance and easy spring cleanup that comes with totally cutting back perennial plantings while the more natural, wilder look appeals to others.
The leaves on more tender plants can turn to a dark mush and can look unsightly; so removing them may be appealing. Plants like Monarda, tall garden Phlox, and peonies can harbor disease over winter, so cutting these down to a few inches can help reduce problems next year.
For plants that simply must be cut back, it is wise to wait until after there have been several killing frosts- usually in November. This will prevent stimulating new growth, which can deplete energy the plant needs to make it through winter. Cutting perennials back to fresh growth during the summer months is also an option, and can eliminate the need for more pruning in the fall.
Not to prune
There are many good reasons to go easy on the pruning this fall. One benefit of leaving perennials through the winter is aesthetic. Tall stalks and stems, seed heads, and blades of grass standing above the snow provide interesting texture and color. Snow and icicles clinging to the spent flower heads of sedum look dazzling as they sparkle in the winter sun.
Providing food and habitat for wildlife is another superb reason to leave perennials over the winter. The seed heads of cone flowers, black-eyed susans, and many grasses provide much needed food for birds and the stems and leaves offer cover, resting areas, and nesting material. Butterflies and other beneficial insects might also lay their eggs on foliage, so removing them could mean you’re also removing next year’s generation of butterflies. What a shame that would be!
Some plants can actually do better if they’re not cut back, as leaving the foliage offers winter insulation for the crowns. Furthermore, plants that emerge later in spring might not be visible if they’re cut back, so leaving the foliage gives them the chance to say “I’m here!” in the spring and ensures that they won’t be disturbed or dug up.
Some perennials should not be cut back in the fall – such as heuchera, lenton rose, and creeping phlox. Ornamental grasses are best pruned in the spring especially because of their wonderful winter interest.
Whatever your approach to fall perennial care, it’s a good idea to pull out dead annuals and clean up debris like fallen leaves to prevent destructive pests and diseases from overwintering there. Happy fall!
Submitted by Simone Schneegans.