Smooth Azalea Rhododendron arborescens

Smooth azalea is an erect, loosely branched, woody, deciduous shrub in the Ericaceae (blueberry) family and native to eastern North America. In its native habitat, it is found growing in sloped woodlands, along streambanks, and sometimes boggy areas. The genus name derives from the Greek words rhodo, which means rose, and dendron, meaning tree.

It requires full sun to partial shade in sandy soil with an acidic pH. Moist soil with good drainage is preferable. Fast growing and spreading by underground runners, smooth azalea can reach a height and width of 8 to 12 feet, occasionally reaching 20 feet.  Its shallow roots do not like cultivation around them, but rather prefer a thick layer of organic mulch that will help maintain moisture and protect against low winter temperatures. Deadhead immediately after bloom to maintain appearance. 

Smooth azalea offers multiple seasons of interest. Pink or yellow fragrant flowers bloom from late spring to early summer and attract bees, butterflies, and hummingbirds. In the fall the foliage turns bright orange to crimson or purple color. The plant tolerates damage by rabbits but is frequently damaged by deer. Plant smooth azalea in mixed or shrub borders, woodland or open shade gardens, pollinator or rain gardens. 

Prune rhododendrons and azaleas after they bloom to preserve the current season's bloom, and allow time for the plant to produce flower buds for next year's bloom.  Rhododendrons and azaleas set next year's flower buds by mid to late summer. 

Insects, Diseases, and Other Plant Problems:  Insect problems include  aphids, borers, lace bugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips, and whitefly. Disease problems include but are not limited to canker, crown rot, root rot, leaf spot, rust, powdery mildew. Full sun can scorch foliage. 

While rhododendrons remain very popular for landscape use, many cultivars are susceptible to Phytophthora root rot—this leads to leaf loss, reduced vigor, branch dieback, and wilting. Implement good cultural practices first, such as improving drainage with organic matter or berms and avoiding overwatering or overfertilization. However, if you have a site with a history of this disease, consider planting a root rot-resistant alternative species. 

The Clemson Cooperative Extension Home and Garden Information Center has a factsheet on common diseases of rhododendron.  

For suitable alternatives, see this video created by Charlotte Glen as part of the Plants, Pests, and Pathogens series.

VIDEO Created by Elizabeth Meyer for "Trees, Shrubs and Conifers" a plant identification course offered in partnership with Longwood Gardens.

More information on Rhododendron.