Preparing a garden for winter involves deciding which herbaceous perennials to cut down and which to leave standing. Cutting back refers to removing dead or dying foliage and stems above the soil line after the growing season ends. This maintenance task is not universal; the appropriate action depends on the specific plant’s health, structure, and overwintering needs. Understanding these requirements ensures the garden remains healthy, reduces pest and disease pressure, and provides structure during colder months.
Perennials That Require Fall Pruning
Specific perennial species benefit significantly from a thorough cutback in the autumn, primarily as a sanitation measure against disease and pests. Plants highly susceptible to foliar diseases, such as powdery mildew, should be pruned immediately after the foliage dies back. Garden phlox and bee balm (Monarda) are prime examples, as their infected leaves harbor fungal spores that reinfect new growth the following spring. Removing this diseased material entirely breaks the pathogen’s life cycle.
Hostas and peonies should also be cut back. Hostas’ collapsed foliage creates a moist overwintering habitat for pests like slug eggs, while cutting peonies to the ground eliminates fungal issues like botrytis blight. This proactive step promotes a cleaner and more vigorous bloom season.
Additionally, perennials that exhibit aggressive self-seeding, such as certain black-eyed Susan varieties (Rudbeckia), can be pruned to prevent unwanted spread. Plants like daylilies (Hemerocallis) are often pruned for aesthetic reasons when their foliage turns slimy after frost. Bearded irises should have their leaves trimmed to remove the overwintering eggs of the iris borer.
Perennials Best Left Standing Until Spring
Many perennials should remain untouched through autumn and winter, offering advantages that outweigh the desire for a tidy garden bed. Leaving the dried stalks and seed heads provides a source of food for birds, such as goldfinches feeding on coneflowers (Echinacea). These structures also contribute to winter interest, adding texture and height to the landscape.
Ornamental grasses, including switchgrass (Panicum) and miscanthus, should not be cut back in fall, as their plumes offer dramatic visual appeal. Upright sedums, like Hylotelephium, also provide structure. The hollow stems of standing dead material provide crucial overwintering shelter for beneficial insects, including native bees.
For marginally hardy perennials, such as garden mums (Chrysanthemum), the spent foliage acts as a natural layer of insulation, protecting the plant’s crown from freezing and thawing. Semi-evergreen plants, like hellebores and heuchera, maintain their foliage through the cold season and should be left alone until early spring.
Timing and Technique for Autumn Cutbacks
Proper timing is essential to ensure the perennial has entered its dormant phase. The ideal moment for most autumn cutbacks is after the first hard, killing frost, which typically occurs when temperatures drop to 28°F or lower for several hours. This frost signals the plant to stop actively growing, allowing energy to be pulled down into the roots for storage. Cutting back too early can stimulate tender new growth that will be killed by subsequent freezing temperatures, weakening the plant.
When executing the cut, use a clean, sharp tool, such as bypass pruners, to avoid tearing the stems. Stems should be cut back to approximately one to three inches above the crown, which marks the plant’s location and offers minor protection. Material removed due to fungal disease or pest infestation must be bagged and discarded, not composted. Tools used on diseased plants should be disinfected between cuts to prevent spreading pathogens.