543 Rhododendron spp.Common Names: azalea, rhododendron Family: Ericaceae (heath Family)
The azalea per se is hard to describe, as it may be a tiny 8" spreading groundcover, or a 20' shrub. There are, in fact, more than 3000 different species, hybrids and cultivars of Rhododendron grown in the U.S. alone. In any case, the azaleas are woody stemmed shrubs, prized for their characteristic, usually prolific, often fragrant, trumpet shaped flowers. These may be only 1/2", or more than 4" across. They come usually in shades of pink, white, purple, orange and red, and may be freckled, variegated, single or double. Many azalea varieties cultivated for landscape use are evergreen, but there are plenty of deciduous ones too. Azaleas are rhododendrons, but all rhododendrons are not azaleas. The common names are often interchanged, but some would restrict "azalea" to those species whose flowers have 5 stamens and use "rhododendron" for the species with 10 or more stamens. Most gardeners use "azalea" for those plants with deciduous leaves and funnel shaped flowers, and "rhododendron" for those with evergreen foliage and larger, bell shaped flowers. Needless to say, the distinctions are not always reliable.
Popular azalea cultivars include the Exbury hybrids (deciduous, spring blooming, showy fall foliage); the Gable hybrids (evergreen, cold tolerant); the Kurume hybrids (evergreen, compact, small flowers); the Indica hybrids (large funnel shaped, unscented flowers, most popular in the SE U.S.); and the Dexter hybrids (evergreen, dense foliage and large flowers). R. kaempferi (torch azalea) is deciduous to semi-evergreen, with pink to red funnel shaped flowers. Like we said, there are thousands of azaleas!
Wild azaleas are found on every continent except Africa and South America. Southwestern China and Papua New Guinea have the most species. Gardeners have been hybridizing different species and selecting azalea cultivars for centuries.
CultureAzaleas must have acidic soil with lots of organic matter. They are shallow rooted so they should be mulched heavily with leaves or pine needles, and you should never cultivate over the root zone. Most azaleas don't need any pruning, but if you do prune, do so immediately after flowering, as azaleas set new buds for the next season soon after they bloom. Light: Full sun to deep shade, depending on species and cultivar. The majority of cultivated azaleas do very well in partial shade. Moisture: Azaleas need a moist soil. They are not tolerant of drought. Most kinds of azaleas do best in the Pacific Northwest where rainfall is plentiful and winter temperatures are not too low. Hardiness: USDA Zones 4 - 9. Hardiness varies greatly among the different species and cultivars. Propagation: Most azalea cultivars are propagated from greenwood cuttings rooted in sand.
With more than 3000 cultivars to choose from, there are a lot of uses for azaleas in the landscape! Azaleas make great hedges and the smaller cultivars are useful as low borders or in beds. Many are outstanding as specimen shrubs. Most thrive in the dappled shade of tall pines.
There are some 800 botanical species of Rhododendron, mostly native to southeastern Asia, with about 30 species in North America. However, no fewer than 3000 different varieties, cultivars and hybrids are cultivated as ornamentals in the U.S. In fact, there are hundreds of azalea societies! Check out the American Rhododendron Society or the Azalea Society of America to see what's happening among azalea enthusiasts.
Florida's native azaleas include, but are not limited to, R. austrinum (flame azalea), which blooms bright orange and is very early flowering; R. canescens, known as Pinxter azalea, which has very fragrant light pink flowers also in early spring; and R. viscosum, or swamp azalea, which blooms in the summer with small white flowers.
Steve Christman 04/02/99; updated 12/04/00, 3/23/02, 2/25/04, 4/14/08