Taken from http://gardening.about.com/od/maintenance/a/Fall_Pruning_3.htm
While it's tempting to cut back the whole flower garden in the fall, even in colder climates, it can be nice to leave some perennials standing throughout winter months. The seeds of Echinacea and Rudbeckia will attract and feed the birds: Sedum will hold onto snow like frosting. There are also plants that like the protection their foliage provides for their crowns. Asclepias (Butterfly Weed), Chrysanthemums and Heuchera (Coral Bells) fare best if cleaned up in the spring.
But some perennials don’t handle rough weather well. They won’t remain attractive after frost and they have recurrent problems with pests and diseases, which will over winter in their fallen foliage and surface in the spring. These perennial flowers are best cut down in the fall. If they are diseased, throw the foliage away, do not compost it.
There will always be exceptions and time will play a factor. No one can really pinpoint when frost and snow will come. Many gardens survive just fine with no attention at all in the fall. Consider this listing and the complementary Plants to Leave Standing Until Spring, as guidelines. You will learn what works and what doesn’t, for your own garden. But it never hurts to take some time and put your garden to bed, in the fall.
Perennial Plants to Prune in the Fall
- Bearded Iris The tall foliage of bearded iris begins flopping early in the season. By fall, it’s cover for iris borers and fungal diseases. Cut back after a killing frost and it would be wise to dispose of the foliage, rather than composting. (Zones 3 - 10)
- 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. (USDA Zones 4 - 9)
- Blackberry Lily (Belamcanda chinensis) Prune to keep the foliage from collapsing and causing the crown to rot and to avoid borers. (USDA Zones 5 - 10)
- 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. (USDA Zones 3- 10)
- Bronze Fennel (Foeniculum vulgare ‘Purpureum’) Bronze Fennel has increased in popularity lately and can be found accenting many gardens. The foliage provides food for swallowtail caterpillars, which can leave the stems completely stripped by fall. If that’s the case, they are no longer providing any useful service and can be cut back to the ground. (USDA Zones 5 - 9)I was surprised that this is a perennial in zone 5. Have any of you had any luck wintering this one over?
- Catmint (Nepeta ) Nepetas respond 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. (USDA Zones 3 - 8)
- Columbine (Aquilegia) Remove any foliage showing leaf miner damage and remove any debris around the base of the plants. Aquilegia send out growth early in spring and appreciate not having the old foliage to contend with. (USDA Zones 3 - 9)
- 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. (USDA Zones 5 - 7)
- Crocosmia (Crocosmia) The flowers of Crocosmia fall of 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 respond well to shearing and unless you are in an area where they remain somewhat evergreen, fall pruning will save you a messy cleanup in the spring. (USDA Zones 3 - 9)
- I will put more in tomorrow's post on the perennials to cut back in the fall. Till next time, this is Becky Litterer from Becky's Greenhouse, Dougherty, Iowa