4. Trees and Shrubs

Especially if they are varietals that won't flower until next spring or summer, fall is a perfect time to invest in some lawn and garden beautification. Retailers count on people losing interest in their yards as the warm weather wanes. But fall is one of the two best times to plant trees and shrubs, and many perennial plants that will flower year after year (early spring is the other, but prices will be higher then). Perennials are always a better bargain than annuals, in the long run, because they will re-emerge year after year.

"A few years ago I bought $900 worth of perennial plants for only $30 – they were already marked down by 80%, but I offered to take everything they had left in order to help them make room for mums, pumpkins and other fall fare," Yeager said. "It never hurts to ask."

It's also a good time to stock up on things like potting soil, pots and other gardening equipment, which is typically discounted, MacEahern said. And if you need a new lawn mower, Fall is the best time to get a deal – preferably on an electric model, to cut down on air pollution, and the asthma attacks it can trigger. But any 2010 or 2011 model should be a whole lot cleaner than the old model in the garage. MacEahern also recommends checking for deals on drip irrigation systems, sprinkling timers, and other devices that can help you keep next year's lawn and garden thriving while using water efficiently.