Rhododendron maximum

Rosebay rhododendron is an evergreen shrub in the Ericaceae (blueberry) family that grows 10 to 20 feet tall. It is native to North America from Ontario and Nova Scotia south to Ohio, Alabama, and Georgia, with a concentration of plants in the southern Appalachian Mountains. The genus name derives from the Greek words rhodo, which means rose, and dendron, meaning tree.

This plant prefers moist, well-drained, richly organic, acidic soils in dappled shade and protection from afternoon sun, which can scorch the leaves. It will not tolerate dense clay, and the roots may rot if the soil does not drain well. Plant the root ball high in the soil to help with drainage. Its shallow, fibrous root system (do not cultivate around plants) will benefit greatly from a mulch of wood chips, bark, or pine needles to help retain moisture and stabilize soil temperatures. Avoid overwatering and over-fertilizing.

Rosebay rhododendron’s habit is upright, loose, and multi-stemmed. The bark is thin, smooth, and light brown on young trees. As the tree ages, thin scales develop. This species blooms later than some, and the flowers attract bees, butterflies, hummingbirds, and other pollinators.

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. 

Rosebay rhododendron does well as an understory shrub planted in groups in woodland or naturalized areas, or as specimens in butterfly or pollinator gardens. As an evergreen it adds interest in a winter garden.

Fire Risk: This plant has a medium flammability rating. 

Insects, Diseases, and Other Plant Problems: Insect problems include aphids, borers, lace bugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips, and whitefly. Diseases include canker, crown rot, root rot, leaf spot, rust, and powdery mildew. This plant is frequently damaged by deer.

While these shrubs 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. 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.