How do you cut back perennials? Some can be cut down after the first killing frost; others can be left to help birds and beneficial insects during the winter months. Let’s talk about which perennials to tackle, which to leave, how to cut back perennials properly, and other ways to prepare your perennials for winter so they survive and thrive next spring.
When to Cut Back Perennials
After several hard frosts, many herbaceous perennials have old foliage and dying stems. It’s a good time to cut down to the ground, allowing the crown (base of plant) to remain dormant over wintertime. Diseases can overwinter in dead and rotting foliage, as can slugs and other pests. Old stems can also get battered about by fall and winter winds which will damage the plants crown and roots.
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.
Not all perennials need to be cut back. Some perennials with seed heads add winter interest and also provide food for birds and wildlife. These can wait until spring to be cut back—when new growth appears.
Which Perennials to Cut Back
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 that can be cut down to the ground in autumn include:
- Bearded iris,
- Day Lily
- Hardy geranium
- Shasta Daisy
How to Cut Back Perennials
To cut back your perennials, remove spent flower stems. Use bypass pruners and make clean cuts at an angle through the stems of the plant. I usually leave 6-inch stubs so I can find the plants next spring.
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.
To prune clump-forming perennials such as hardy geraniums, reduce clumps to the ground level in the fall. Cut away all the dead foliage. Any perennials and grasses that die back can be died up this way in autumn, too.
After cutting back your plants, apply a light mulch. Then, wait to feed until the spring for healthy growth.
Leave Some 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.
Thistles and plants with seed heads also add interest, food, and shelter to wildlife over winter. See plants with seedheads to feed the birds.
Perennials NOT to Cut Back
Some perennials (including the alpines below) and evergreen perennials such as epimediums, hellebores, and euphorbias should be left alone.
Candytuft, primulas, dianthus, hens & chicks, heaths, and heathers are also considered evergreen and should not be cut back in the fall.
Pulmonaria and penstemons should also be left in place until spring.
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 Garden 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.
Weed Before the Freeze
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.