KUSA - If you cut back your garden in fall, you're just asking for trouble. We don't do that anymore; it hasn't been considered a good horticultural practice for at least 50 years. I've never done it.
Cutting back or pruning plants in fall encourages new growth. New growth is vulnerable to winterkill.
This just isn't the right time to be tidy. Perennials are supposed to collapse in on themselves in winter. This helps protect the crowns of the plants. The crown is the center of the plant at the soil surface that is most vulnerable to winter damage. As the leaves of the perennials decompose and crumble over winter, they enrich the soil and feed the earthworms that are so vital to good soil structure.
Pruning spring-flowering trees and shrubs in fall is a big mistake. They've already set their buds. If you prune now, you're cutting off next season's flowers. Certainly don't touch your roses now. Cutting them back is a recipe for disaster. They will put out new growth and the whole cane will die back.
It's fine to pull up annuals and vegetables after frost--in most cases. You may want to leave those that you rely on to self-sow, such as marigolds, calendula, cosmos and sunflowers. Birds rely on the seeds of these plants, as well as those of perennials and ornamental grasses, to see them through the winter.
If you live with someone who gets all tidy in the fall, hide their loppers and pruners. Now is not the time to use them.
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