Korean Rhododendron Rhododendron mucronulatum

Korean rhododendron is a woody, deciduous shrub in the Ericaceae (blueberry) family.  Its form is twisting, multistemmed and open and it has spectacular, showy, pink flowers that appear in late winter to early spring before its diamond-shaped leaves appear. Native to northeastern North America, it grows at a relatively slow rate to 4 to 8 feet tall and wide. The genus name derives from the Greek words rhodo, which means rose, and dendron, meaning tree.

This plant prefers moist, well-drained, acidic soils in dappled shade and protection from afternoon sun, which can scorch the leaves. Korean rhododendron is extremely cold hardy.  It does not tolerate dense clay, so if you have clay soil, amend with organic material. Plant the root ball high in the soil to help with drainage issues. Avoid overwatering and over-fertilizing.  Mulch each year to keep the roots cool.

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. 

Korean rhododendron can be used as a cultivated, woody shrub in a mass planted in a woodland or natural area or as a specimen that will attract hummingbirds and bees to a pollinator garden.  It works well in a shrub border or as an accent plant and is attractive when planted near other early spring bloomers like daffodils and crocus.  

Insects, Diseases, and Other Plant Problems:  Insect problems include aphids, borers, lacebugs, 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. Early flowering makes it susceptible to spring freezes.

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. 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.