Prepare your perennials for winter! Most perennials can be cut down after the first killing frost; others can add interest or help birds and beneficial insects during the winter months. See our tips.
CutTING BACK Perennials
After several hard frosts, most perennials can be cut back. To cut back your perennials, use bypass pruners and make clean cuts through the stems of the plant. I usually leave 6-inch stubs so I can find the plants next spring.
Plants need to be cut back after frosts to avoid disease and pest problems in the spring. Bee balm and phlox are prone to powdery mildew so cut them all back once they’re gone. Remove all hosta after a hard frost, including any leaves on the ground, as they harbor slug eggs. Other perennials to cut back include bearded iris, peony, daylily, veronica, sunflower, salvia, shasta daisy, clematis, columbine, catmint, and yarrow.
Don’t be in a rush and be sure until a few hard frosts. Even if the flowers or leaves are dead, the roots are reclaiming energy from the dying plant for healthy growth in the spring.
Leave Some Winter Interest
Leave a few things standing for winter interest. The blackberry lily Belamcanda looks great until heavy wet snow finally knocks it down. Ornamental grasses add movement and sound to the landscape. I let the agastaches and coneflowers and rudbeckia stand for the birds to enjoy. Self-seeding plants will provide you with volunteers next spring to move to new spots or share with friends.
Many perennials, like this penstemon, have already started to form leaves for next year at the base of the plant. When cutting back be sure to leave these rosettes of green.
Some Perennials NOT To Cut
Some perennials (including the alpines above) and epimediums, hellebores, candytuft, primulas, dianthus, hens & chicks, heaths, and heathers are considered evergreen and should not be cut back in the fall.
This hellebore is considered an evergreen and should not be cut back in the fall.
Do not cut back marginally hardy perennials such as garden mums (Chrysanthemum spp.).
Clean Up Debris
As with the vegetable garden, any diseased or bug infested plant material needs to go—far away. Don’t put it in the compost pile. Debris from things like rusty hollyhocks, peonies with powdery mildew, leaf-spotted delphiniums, and other fungal-infected flowers should be removed from the garden.
Leaves from a peony infected with powdery mildew should not be composted.
Don’t Fertilize in the Fall
Fertilizing in autumn encourages new growth that will just get killed when cold weather hits. Compost is not considered a fertilizer; it is a soil conditioner so feel free to add that in the fall. If your soil test indicates that you need lime, it can be applied in the fall also.
Before the ground freezes, do a final weeding. The more weeds you can get out now, especially those that have seeds, the fewer weeds you’ll have to deal with in the spring. Edge your beds for one last time and you’ll start the year with a neat and tidy look.
To Mulch or Not to Mulch
If you are growing plants that are hardy in your zone and live where snow cover is plentiful each winter you probably don’t have to worry about mulching your garden, though it’s always insurance to give them some extra protection. It’s newly planted perennials that are the exception. Definitely tuck some mulch around them for their first winter.
The purpose of a winter mulch is to keep the soil temperature even and prevent heaving of roots due to alternate freezing and thawing of the ground. Waiting until the ground is frozen before mulching is not only best for your plants but also discourages rodents from making a cozy home there. Use a mulch that does not pack down and smother your plants. Shredded leaves, pine needles, straw, or evergreen boughs are good choices. Snow provides the best insulating mulch, it goes down gradually and melts gradually.
Watering the Garden
If you live where it has been dry this growing season, keep watering your garden until the ground freezes. Usually there is plentiful moisture in the fall but many areas experienced drought conditions this summer and the ground is dry. Plants that are water stressed will have a tough time surviving the winter.
The more work you do in your perennial garden this fall, the less you’ll have to do next spring.