The Q&A Archives: Fall Care for Mildewed Perennnial Sweet Pea

Question: I have several perennial sweet peas that climb up a trellis on a garden shed. This past summer, despite my best efforts they developed powdery mildew. I'm not sure what type of fall clean-up I should pursue. Should I wait until there is a frost and cut the vines down or should I wait until spring to cut back? Also, do I need to wash/clean the trellis and shed to insure the powdery mildew doesn't harbor over the winter?

Answer: When the plants have stopped growing, trim away the old stems at the base. Remove all of the "plant debris" and destroy it to reduce the possibility of reinfection. You might also add a fresh layer of mulch. During the growing season, do what you can to increase air circulation around the plants (thinning them a bit rather than allowing a wild heavy thick tangle to develop might help) and avoid wetting the foliage, especially in the evening. In my experience, mildew just reappears on some plants some years (it can blow in on the wind) and unfortunately washing the inanimate objects would probably not help.

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