Knaphill Azaleas Rhododendron hybrids

Exbury azaleas are deciduous shrubs in the Ericaceae (blueberry) family. The genus name derives from the Greek words rhodo, which means rose, and dendron, meaning tree.

Exbury azaleas have an upright, open spreading habit.  Large showy flower trusses explode in the spring with a wide variety of vibrant colors.  The flowers are similar to the flame azalea.  The showy leaf color provides fall interest.

These plants prefer moist, well-drained, acidic soils in dappled shade and protection from afternoon sun which can scorch the leaves. They do not tolerate dense clay, so if you have clay soil, amend with organic material. The roots may rot if soil does not drain well. Plant the root ball high in the soil to help with drainage issues. Avoid overwatering and over-fertilizing. They are very winter hardy and have a moderate growth rate. Pruning, if desired, may be done after flowering. 

These shrubs are excellent for naturalizing and are at home as understory shrubs planted in groups in woodland gardens, or as specimens in pollinator gardens where the flowers will attract hummingbirds and bees.

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.  However, if you have a site with a history of this disease, consider planting one of the root rot-resistant alternative species listed in the left-hand sidebar.

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.