Begin Dividing Perennials
If some of your perennials seem to be producing fewer flowers, especially in the center of the clump, it's likely that they need dividing. Choose a cool, cloudy day, and dig up the entire root mass. Cut the rootball into several chunks, and replant the pieces or pot them up in containers to share with friends.
Root cuttings of coleus, geraniums, and herbs to bring indoors over the winter. Cut a 3-inch section of stem, remove the bottom half or two thirds of the leaves, and place in moist soilless mix, vermiculite, or sand. (Some gardeners dip the cut ends in rooting hormone; others find this unnecessary.) Place the entire container in a loosely tied plastic bag to maintain humidity.
Fall is a good time to renovate bare spots in your lawn. The cooler temperatures encourage good germination and root growth of cool-season grasses. Be sure to choose a variety appropriate for your region and conditions (for example, sun or shade). Prepare the area by raking thoroughly, then adding a thin layer of compost or topsoil. Cover newly seeded areas with a row cover or a light scattering of straw to keep birds from eating the seed, and keep it well watered.
Place orders now for garlic for planting this fall. There are numerous varieties, each with subtle flavor and growth characteristics, so consider experimenting with something unusual. Don't plant garlic from the grocery store because it may have been treated to prevent sprouting, and it may not be adapted to your growing region. Plant your garlic shortly after the first hard frost to allow the garlic enough time to develop strong roots before winter.
Help Roses Enter Dormancy
Stop pruning roses now to help them prepare for their winter dormancy, and this includes deadheading. By allowing any remaining flowers to develop into rose hips, you'll help signal to the plant that it's time to wind down for the season.