Azaleas are an evergreen shrub and a type of rhododendron. Smaller than other rhododendrons, azaleas provide an abundance of blooms in shades of red, pink and white.
While azaleas are a type of rhododendron (and may be called rhododendrons) and thrive in similar climates, soils and care, there are differences. To distinguish between the two plants, look first at the leaves. Rhododendrons have large, leathery, blue-green leaves with sometimes brownish undersides. In contrast, azaleas have glossy leaves of a deep green and feature small hairs on the leaf surface. Azaleas also have single flowers instead of clusters like rhododendrons. Rhododendrons are not limited to pinks, reds and whites, and may have a spicy scent in addition.
Azaleas usually bloom in March or April. New cultivars have been developed that bloom later (into May and June) and a new type -- Encore -- flowers twice, in both spring and again in the late summer, states North Carolina State University. Since most azaleas bloom only once a year, for about two weeks, planting several varieties of azaleas allows you to enjoy a profusion of blooms for a longer period, as The Augusta Chronicle notes.
Another factor influencing bloom time, on top of the azalea type, is the USDA growing zone -- or more accurately, the weather. "Actual bloom dates may vary a week or two either way," explains the Azalea Society of America, with blooms erupting earlier in warmer weather. Warmer zones also encourage a second bloom in the fall in some azaleas, if it is warm enough.
With sufficient moisture, flower buds for next year's blooms form during early summer. However, azaleas must have four to eight weeks of temperatures below 10 degrees Celsius in the winter to bloom well. Without this cold weather they will bloom for a longer time, but sporadically, instead of simultaneously.