Northern & Central Midwest
Leave Perennial Seed Heads
It's fine to remove soggy perennial foliage in the fall unless it bothers you, but leave seed heads on through the winter. Birds will feed on these seeds, particularly on members of the daisy family, like purple coneflowers, black-eyed Susans, coreopsis, zinnias, and marigolds. When in doubt, leave the seed head you can always remove it in spring.
Begin Fall Pruning
Once deciduous trees and shrubs begin to lose their leaves, you can do light pruning. It's easier to see the shape of the plant without leaves. Prune to shape if necessary, cut out crossing or damaged branches, and be sure to make cuts right at the branch collar to avoid stubs.
Clean Out Weeds From Around Vegetable Garden
Since many viral diseases can overwinter in weed roots, start eliminating them from areas near vegetable and flower gardens. Weeds left through the winter make great overwintering spots for insects such as flea beetles, Mexican bean beetles, and squash bug larvae. Remember that vinegar or hot water poured on the crown makes a great herbicide.
Dispose of Diseased Foliage
Blights and viruses that attack tomatoes, peppers, and beans spend their winter as dormant spores in diseased foliage. Unless you have a really hot compost pile, send the debris off to the city compost where you can be assured the fungal spores will be killed so they won't be around to infect next year's tomatoes.
Finish Fall Planting
Try to have trees, shrubs, perennials, and bulbs planted by the time all the leaves have fallen (except bare-root plants). As the ground cools and freezes, roots also slow their growth. Plants that haven't developed strong roots may not survive the winter.