The plant nurseries that were jammed in the spring with shoppers this spring eager to turn over the newly-thawed soil, are now quiet, and few owners want to go into winter with a stock of landscaping plants vulnerable to freeze and disease. This makes September, October and even Novemer months to watch for some great deals on trees, shrubs and ground cover, often more than 50% off.
In mostly zones of the U.S., fall is a great time to plant new landscaping. The threat of parching heat is past and a deep, prolonged freeze still a couple of months away. Most plants will respond well if planted in the proper soil, with some compost or other nutrients and adequate water. The slow cool down of fall will allow them to slip into dormancy and return in the spring ready to add color and interest to your yard and garden.
Be sure to check the latest revision of the USDA Hardiness Zone Map for what plants will thrive in your area, and learn to recognize a promising tree or bush from one on life support. If you're not confident, stick to shopping at reputable nurseries rather than mass merchandisers.