Azaleas and Rhododendrons

WITHIN THE GENUS Rhododendron, azaleas and rhododendrons are divided into many groups. There are no clear-cut lines that distinguish all azaleas from all rhododendrons, but here are some ways to help you differentiate them:

Start with the leaves. Azaleas have small leaves that are usually pointed and narrow; most rhododendrons have large leaves that are long, broad, and leathery. One group of rhododendrons, the small-leaf (lepidote) evergreen rhododendrons, has smaller leaves than those of the average azalea, but the lepidote leaf is thicker and blunt at the tip.

Next, look closely at the flowers. Azalea blossoms are usually funnel-formed with five stamens; flowers appear all over the bush in profusion. Rhododendrons bear their flowers in trusses (large clusters of individual blossoms), and each blossom is more bell-shaped and larger than the azalea bloom.

Where do they grow? There are important differences in climate range, too. The two main azalea groups, evergreen and deciduous (varieties that drop their leaves in fall), can be found in nearly every part of North America, from the frosty Canadian plains where it reaches -45°F to tropical Florida. Rhododendrons are fussier. They like environments where it is neither too hot nor too cold, generally preferring Zones 5 to 8. However, in the last year or two, several new rhododendrons have been bred to withstand -35°F temperatures without destruction of flower buds. The hotter climates still are a problem for rhododendrons; in the South and Southwest, the plants develop deadly diseases and bloom scantily or not at all, because they need a certain amount of chilling to develop strong flower buds.