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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - November 13, 2013

From: Rockville, MD
Region: Mid-Atlantic
Topic: Diseases and Disorders, Seasonal Tasks, Wildflowers
Title: Cutting Back Perennials in the Fall?
Answered by: Anne Van Nest

QUESTION:

We have large beds of flowering native perennials that we planted around our house as part of a landscape conservation plan (various Joe-Pyes, goldenrods, turtlehead, blazing star, brown-eyed Susans). Fall is upon us in Montgomery County, MD, and we see lots of birds having a great time kicking around in the leaves from the trees that are littering the beds. In the past we've cleaned the beds out down to the mulch layer before winter, but I'm starting to wonder if this is best for the plants and animals. Do we have to clean out the tree leaves before winter to keep the plants healthy? Can we leave them, or will this promote too much disease?

ANSWER:

The only parts of the garden that really need to be cleaned up well (down to the mulch or even replace this too) are any area around a seriously diseased plant. While native plants are generally disease and pest free, some problems like powdery mildew on phlox, leaf spot on bugbane, or overwintering leafminer on gaillardia could be serious enough to harm the plants. In this case all the affected foliage should be removed so that the fungus spores or insect eggs and pupa do not overwinter.  For the rest of the garden, healthy woody perennials can often be left intact or pruned to 6 inches for the winter.  Any seeds or insects still on the plant will be welcome food for the wildlife and the uncut stems will help collect insulating snow around the plant and give it extra protection as well as mark where the plants are located next spring.
Any fleshy perennials though (like touch-me-nots) should be removed in the fall since they will turn into a mushy mess after the first frost.
Leonard Perry of The University of Vermont Extension has posted a good information sheet on Fall Perennial Care online.

 

From the Image Gallery


Joe-pye weed
Eupatoriadelphus maculatus

Ohio goldenrod
Oligoneuron ohioense

Pink turtlehead
Chelone lyonii

Ontario blazing star
Liatris cylindracea

Black-eyed susan
Rudbeckia hirta

Fall phlox
Phlox paniculata

Indian blanket
Gaillardia pulchella

Jewelweed
Impatiens capensis

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