Perennials to Prune in the Late Summer and Fall
Readying your garden for winter is important to the health of your plants. How and when you cut things back is determined by the individual needs of your plants, your desire to provide food and cover for wildlife, and your appreciation for winter interest.
Below is a guideline on which perennials to prune in the late summer and fall:
- Bearded Iris The tall foliage of bearded iris can begin to flop early in the season. Creating cover for iris borers and fugal diseases. Cut back late in the summer. It would be wise to dispose of any diseased foliage, rather than composting.
- Beebalm (Monarda didyma) Even the most resistant varieties of Monarda can succumb to mildew. When that happens, you’ll be cutting them back long before fall. Fresh, new growth can be left on until spring. Sometimes selective thinning of the stems is all that is needed and you can leave the remaining seed heads for the birds.
- Blackberry Lily (Belamcanda chinensis) Prune to keep the foliage from collapsing and causing the crown to rot and to avoid borers.
- Blanket Flower (Gaillardia x grandiflora) Gaillardia is a pretty hardy plant, but cutting back the spent stems seems to improve its hardiness even more, by improving its vigor.
- Catmint (Nepeta) Responds well to severe pruning throughout the season. The foliage will be damaged by winter cold and will need to be cut back anyway, so get a head start by pruning in the fall.
- Columbine (Aquilegia) Remove any foliage showing leaf miner damage and any debris around the base of the plants. Aquilegia sends out growth early in spring and appreciates not having the old foliage to contend with.
- Corydalis (Corydalis lutea) It’s hard to kill Corydalis, but if you’d rather cut back on it’s enthusiastic spreading habit and it hasn’t been deadheaded during the summer, cut it back after a killing frost.
- Crocosmia (Crocosmia) The flowers of Crocosmia fall off naturally once blooming has finished and the seed heads can offer interest, but the foliage eventually heads downhill and there is nothing to be gained by leaving it up through winter.
- Daylily (Hemerocallis) Daylilies can use a general removal of old leaves late in the summer. Wait till late fall to cut to the ground.
- False Sunflower (Helianthus) By this time Helianthus foliage isn’t a standout and by the time the flowers have faded, it’s also time to cut the plants down.
- Golden Marguerite (Anthemis tinctoria) By late summer, Golden Marguerite daisies have finished blooming and are nodding off. Pruning to the crown will encourage new basal growth that helps protect and sustain them through the winter.
- Goldenstar (Chrysogonum virginianum) Often has problems with powdery mildew. If so, remove and destroy foliage in the fall.
- Hardy Begonia (Begonia grandis) Frost will blacken and collapse the foliage. If left at the base of the plant, it can cause crown rot. Prevent this by cutting back in the fall.
- Helianthus (Perennial varieties) H. x laetiflorus, H. salicifolium…) The perennial members of the sunflower family usually finish blooming toward the end of summer and go down hill from there. Deadheading does not improve their appearance and the tall stems are guaranteed to break and flop. Cut back to ground for aesthetics.
- Hollyhock (Malva alcea) See Macleaya cordata.
- Japanese Anemone (Anemone x hybrida) The foliage of Japanese Anemones turns black and is very unattractive with frost. Unless your Japanese Anemones have had a very good year, it’s advised to cut them back in fall.
- Ligularia (Ligularia dentata) is predominantly grown for its foliage, which turns to a dark mush after frost. Feel free to cut it back.
- Lilyleaf Ladybell (Adenophora lilifolia) Can be cut back after flowering diminishes. Basel foliage will remain fresh until spring.
- Masterwort (Astrantia major) Masterwort is often deadheaded throughout the summer, to prolong the bloom time. If conditions are dry, the foliage will begin to yellow and it can be sheared to the crown. Allow the new growth to remain through the winter. If no yellowing occurs, leave the plants for spring cleaning.
- Meadow Rue (Thalictrum aquilegiifolium) Performance wise, it doesn’t really matter when Meadow Rue is cut. Since it’s done flowering for the season, pruning in the fall leaves one less to do in the spring. Some varieties will self-seed. If that’s desired, let it go until spring.
- Mountain Bluet (Centaurea montana) Mountain Bluets tend to become black and unsightly with the first frost and can be cut back in the fall. However, if you shear them back in late summer and only basal growth is present, you can allow that to remain.
- Penstemon (Penstemon barbatus) Penstemon don’t like wet feet and should be planted a little higher in the ground than most plants. The foliage usually declines toward the end of summer and can be trimmed back, inducing new basal growth. Mulch the plants through winter.
- Peony (Paeonia) Peonies need a period of cold to set buds for the following season. That coupled with the fact that their foliage is extremely prone to mildew is reason enough to remove the foliage in the fall. Infected foliage can be removed and disposed of in late summer. Healthy foliage will turn golden in fall and can be removed once it has turned after the first frost.
- Phlox (Phlox paniculata) Phlox is prone toward powdery mildew. Even resistant varieties can become infected in bad weather. If so, prune & destroy all foliage and stems in the fall.
- Plume Poppy (Macleaya cordata) Try and kill a Plume Poppy, I dare you. Cut these back before they go to seed or you will have Plume Poppies everywhere.
- Salvia (Salvia nemorosa) Perennial Salvia benefits from several prunings during the growing season. In fall when blooming slows, cut the plant back to the new basal growth.
- Siberian Bugloss (Brunnera macrophylla) Fall clean-up is preferable. This emerges early in the spring a will appreciated a clean area.
- Sneezeweed (Helenium autumnale) Doesn’t finish blooming until mid-fall. The foliage can be cut back and removed when it’s done blooming.
- Solomon’s Seal (Polygonatum odoratum) Although listed here, Solomon’s Seal pretty much disappears on its own, after a frost or two. Certainly the leaves will drop. If the stems remain, they can be pruned back to the ground.
- Speedwell (Veronica spicata) As flowering ceases, the plants can be sheared to the ground. They will only turn black and ugly if left until spring.
- Wild Indigo (Baptisia australis) Baptisia is one of those plants that splits in the middle if not sheared back after pruning, however many gardeners like the seed pods and simply stake the plants. Come frost, the foliage turns black and even staking isn’t going to help its appearance. Cut back for aesthetics.
- Yarrow (Achillea) Achillea doesn’t like to sit in cold, wet soil. By fall, most of their blooms are spent and the foliage is flopping and possibly diseased. Cut back in early fall and new basil growth with fill in before frost.