Azaleas are evergreen shrubs that usually produce their flowers in spring or summer. They belong to the same genus as the rhododendron and have a similar appearance, although azaleas are smaller plants. Many species exist and even more hybrid varieties are available at nurseries. The Azalea Society of America website reports that over 10,000 different types of azalea plants have been identified.
The Azalea Society of America states on its website that the cultivars called "Encore" have been specially bred to provide fall blooms, especially in colder climate zones. The website Encore Azalea claims that this azalea is the best selling brand of azalea. It blooms in spring, summer and fall, depending on the exact cultivar, of which 24 exist. Ten of the Encore varieties are cold-hardy to U.S. Department of Agriculture plant hardiness zone 6. Spring weather can influence the time of year when any azalea blooms: when weather is cooler, blooms will occur one or more weeks later than during years when the spring is warmer.
Plum Leaf Azalea
The azalea known as Rhododendron prunifolium, or plum leaf azalea, is a native species and is one of the latest blooming varieties of this plant, according to the Azalea Society of America. It often produces its flowers in June and again well into September, depending on the climate zone in which you grow it. Occurring naturally in a small area of eastern Alabama and southwestern Georgia, where it is classified as threatened, its flowers are orange to bright red and large — up to 2 inches in diameter. Flower size and color vary, depending on the growing location.
The Le-Mac Nurseries in Hampton, Va., tested this standard variety of azalea in two different environmental situations and concluded that those grown under shade cloth did not bloom in fall, but those that received sun produced some flowers in fall. A lack of water might have accidentally caused this occurrence: the nursery’s automatic watering system was reportedly broken and the plants grown in sunny conditions should have received more irrigation than they received. Dr. Sandra McDonald, author of an article titled "Fall Bloom of Rhododendrons" in the Journal of the American Rhododendron Society, believes that such dry conditions contributed to early bud set.