Sow seeds of fast-maturing greens, such as spinach, for a harvest well into fall. A simple cold frame, made from straw bales covered with old windows, will extend the season further into the winter.
Prune Dead Branches
Avoid heavy pruning on most trees and shrubs in fall, but do go ahead and remove dead branches and limbs that could pose a hazard during strong winds.
Allow Rose Hips to Form
You've been diligent in deadheading your roses to promote more bloom. Now it's time to stop and let nature take its course. By allowing spent roses to remain on the plant and develop into the fruits, called hips, you'll encourage plants to begin entering dormancy. If you continue to deadhead, plants will respond by sending out new growth, which will be susceptible to damage by early fall frosts.
Plant garlic four to six weeks before the first fall frost date. Fall-planted garlic yields much better results than spring-planted crops. Avoid planting grocery store garlic, because it may have been treated with sprout inhibitors. Rather, purchase garlic that sold specifically for planting, or plant organic garlic, preferably bought from a local farmer since you'll know it's adapted to your climate.
Prepare New Garden Beds
Dig new garden beds in preparation for planting next spring. Till the area and incorporate organic matter, such as leaves and grass clippings. Plant a cover crop -- barley, winter rye, and/or Austrian peas -- to suppress weeds, minimize compaction by winter rains, and further increase organic matter when you till it in next spring.