To Cut or Not to Cut?
What to Cut Back in October and What to Leave Until Next Year
By Charlene MacKenzie
Ready to do some fall clean-up around your yard? Check our green light/yellow light/red light lists below for what to cut back, what to trim, and what to leave alone.
Start with clean, sharp pruners, a good supply of yard bags, and gloves. Pick a dry, sunny or overcast day to do your fall garden clean-up. Don’t prune anything in hot, freezing, or very windy weather - it’s more stressful for the plant and dries it out too much. Safety first: Take a walk around your yard to scout for any issues: hornet nests, poison ivy, hoses or electrical wires where you’ll be cutting. Once a “hard” or killing frost arrives, usually early to mid-October in the Niagara region, most perennials can be cut to or near the ground, with notable exceptions (ornamental grass and tree peonies, for instance). After cutting back perennials, let the stem stubs “cure” in the fall air to naturally seal before topping them with any compost or mulch, if using.
Later, when the leaves have fallen from the trees, don’t throw all that free material away! Rake some into your garden beds to act as a winter mulch. Run your lawnmower over
piles of dry leaves to “mulch” them into your lawn. If you compost, save a couple of paper yard bags of dry maple or oak leaves over the winter to act as the “brown” compost ingredients when you have too much of the “green” ingredients in spring.
If applying a fresh layer of mulch in fall, keep it a couple of inches away from the base of living plants to prevent trapping moisture against stems. Once the ground begins to freeze, it’s fine to mulch over cut-back plants to help protect them through winter. Pull mulch away again when they emerge in spring.
PERENNIALS
Green Light (Cut Away!)
Garden Peonies: Cut to ground level (NOT for tree peonies). Remove all cut stems and fallen leaves and remove. This can be done even earlier in the season if powdery mildew is present. Discard of any diseased plant material rather than compost it. Don’t put mulch or compost over the stem stubs – bare-earth sun exposure in spring is important for peonies crowns to trigger flowering.
Tall/Garden Phlox: Cut to 1-2” high when flowering is done in fall. Healthy stems can be composted, but if there’s powdery mildew, remove all stems and fallen leaves and discard them.
Bee Balm (Monarda): Same as for garden phlox.
Daylilies: Reblooming varieties such as Stella d’Oro may still be blooming, but for those that have finished, cut stems to 2-3” high and clean up any dead leaves at plant base.
German/Bearded Irises: Cut leaves into “fans” about 3-4” high. Remove any brown or yellowed leaves. Don’t cover the top surface of the roots (rhizomes) with soil or mulch, as this type of iris likes to have its back in the sun to perform best.
Daisies: Cut stems to 2-3” above the ground. Leave any basal rosettes of leaves as they’ll form the basis of next year’s plant.
Tickseed (Coreopsis) and Blanket Flower (Gaillardia): Cut these perennials back to 2-3: high. Remove any dead or diseased stems, but leave any new basal growth intact.
Foxgloves and Hollyhocks: Remove any yellowed, dead or diseased foliage. Cut back flower stems after flowering, but leave any green basal foliage intact. Cut rather than pull – these have shallow root systems and the whole plant is likely to come up with the foliage.
Hostas: Cut back spent flower stalks now, but leave the green living foliage until after the first hard frost turns it soft and yellow. They pull up rather than cut the dead leaves. This helps prevent crown rot. Let stem stumps dry, then add a layer of mulch.
Yellow Light (Light Trim)
Lavender, thyme and other woody perennials: Trim back spent flower stems on lavender, and trim about 25 per cent of the soft green plant material from the top of the plant. Don’t cut back the woody parts of the plant, that’s where next year’s growth starts.
Siberian Irises: Go ahead and cut back the flower stems when they finish flowering in summer. You can cut the foliage back in fall if you have very sharp pruners, but it’s much easier to cut in spring after winter has softened the tough leaves a bit.
Coneflower (Echinacea) and Black-Eyed Susan (Rudbeckia): Fall clean-up of these late-flowering perennials depends on how wildlife-friendly you want your garden to be. While flowering, they provide late-season food for pollinators, and when they go to seed, they’re food for goldfinches and other birds. If you want a tidier look, one option is to deadhead spent blooms until mid-September and leave the later flowers to go to seed. Another is to simply cut back the flower stems after the main flowering time and leave the foliage to feed the roots until frost hits.
Upright Sedum (Autumn Joy, etc.): Leave sedum standing and flowering until after stems are killed by frost, as bees and other pollinators rely on these plants that can stay in flower to November. After frost, they can be cut back to the ground for a tidy and bare garden, but the dried flowers left standing add winter snow interest.
Red Light (Don’t Cut!)
Tree Peonies: Remove dead leaves and petioles but leave the woody stems intact. Discard any diseased plant material rather than composting.
Ornamental Grasses: Don’t cut these back to the ground in the fall, as that would expose the crown (base). New grass grows out of the base of last year’s stem, and too much direct exposure to wet cold can kill or damage it. If there are a lot of broken tall stems, cut the tops but leave at least a foot or two of stem. A better option is to bundle the standing uncut stems with twine into sheaves to look tidy and insulate the crown. Cut to 1-2” in late April.
SHRUBS
Green Light (Cut Away!)
Suckers from shrubs and trees: Some shrubs, such as dogwood, lilac, forsythia and willow, as well as some fruit trees and standards (shrubs grafted to taller stems) develop suckers at the base in late summer. Cut these as close to the ground or the base of the main stem as possible. Suckers can take energy away from the main plant, so October is a good time to rein them in before next season.
Yellow Light (Light Trim)
Roses: Do a mild prune to shorten tall canes and any weak, broken or crossing stems. Remove and dispose of any diseased leaves (blackspot). Save the heavy pruning for early spring. Clean pruners with rubbing alcohol between plants.
Hydrangeas – ONLY Smooth (Arborescens) and Panicle: Hydrangeas that flower on new wood can be pruned lightly in fall. Mainly this will be the smooth hydrangeas such as Annabelle and Incrediball varieties. Cut only about a third of the height of the smooth hydrangea – cutting back hard will result in weak, floppy growth the next year. For panicle hydrangeas (full-sun varieties such as Limelight and Bobo), lightly prune only to control size and shape, and to remove any weak interior stems. Hard pruning could result in winter dieback of flowering stems.
Raspberry and Blackberry Bushes: In fall, cut older canes than have fruited (they’re usually grayish with peeling bark) but leave the green springy new canes – they’ll fruit
next year. Fall’s a great time to tie up any floppy new canes to stakes or along string lines.
Clematis Vines (Group 3 varieties only): Late-blooming clematis in Group 3 such as Jackmanii and Sweet Autumn bloom on new wood and can be cut back in October to about 18” high.
Red Light (Don’t Cut!)
Evergreen Shrubs (Boxwood, Yew, Euonymus, Conifers): Trim any dead, damaged or diseased stems, but leave pruning until spring to avoid exposing freshly-cut ends to “winter burn.” However, clean up any needles or leaves from the ground around them and provide a deep watering to prepare them for winter.
Rhododendrons and Azaleas: Spring-blooming shrubs such as these should be pruned in spring after flowering. Hard pruning in fall could trigger late new growth andlead to winter burn and dieback. After flowering, remove spent flowers and prune, but remember they have a post-bloom “ugly duckling” period before flushing out with summer growth.
Forsythia: These early bloomers can be cut back right after flowering to control their size, but doing so in fall will compromise next year’s bloom.
Lilac: These fragrant May bloomers set next year’s flower buds soon after flowering, so pruning hard in fall will cost you many of next year’s blooms. Instead, deadhead and prune in spring, within a couple weeks of the end of flowering time.
Hydrangeas - Bigleaf (Macrophylla), Mountain (Serrata), Oakleaf (Quercifolia) and Hybrids such as Fairytrail Bride: Most hydrangeas should not be cut back in fall, especially these varieties, as it will compromise the next year’s flowers. During the growing season, deadhead spent flowers at the base of the flower. Weak, dead or broken branches can also be removed. In late spring, after new leaves have emerged on both old and new stems, cut dead stems back to the next set of healthy leaf buds. Hydrangeas that are pruned too hard will overcompensate but pushing out weak growth that results in floppy flower stems that bend after rain and wind.
Japanese Maple and Magnolia: Removed any dead or diseased stems and leaves, but leave pruning until next year. Prune maples either in early spring before buds begin to open (to avoid sap leakage), or in early summer after they’re fully leafed out.
Clematis Vines (most types): Clematis vines that bloom in spring (Group 1) or summer (Group 2) should not be cut back in fall. Most clematis varieties Country Basket carries are Group 2. They bloom first on old wood and then again on new wood. Prune lightly in early spring to shape them and remove weak growth, then prune after blooming if needed. Group 1 varieties bloom on old wood so shouldn’t be cut back in fall. If any pruning to control size is needed, wait until after the spring bloom.
If you have any further questions please feel free to stop in to speak to one of our knowledgeable staff or contact us.
