Brown Leaves and Bare Branches on My Rhododendrons

Basics

• Rhododendrons have large, leathery leaves that stay green in the winter. In spring, they produce flowers in numerous colors, including white, lilac, purplish-pink and red, depending on the variety. Some rhododendrons produce blooms of solid colors, while others have spots or other markings in another color. In addition, some varieties are heat tolerant while others are cold tolerant, so it is best to plant a variety that is recommended for your area.

Phytophthora Dieback

• Several things can cause rhododendron leaves to turn brown, but only a few also cause the leaf to drop off. One of them is dieback caused by the Phytophthora fungus, which most commonly affects container plants. Phytophthora dieback causes a deep brown to black discoloration of the leaves before causing them to fall off, leaving the branches bare. The fungus can become a problem during wet weather in hot summer months. Shaded plants and overhead sprinklers in nurseries provide ideal conditions for the fungus. Inspect any plants for symptoms when purchasing a rhododendron. If you have the fungus at home, you can selectively prune it out of larger plants if you find it early enough. Aggressively prune all discolored, diseased wood in the stems, trimming back to a healthy branch, and destroy all the cuttings, according to North Carolina State University.

Iron Deficiency

• An iron deficiency in the soil can also cause leaves to turn brown and fall off, leaving bare branches on the rhododendron plant. However, those are the symptoms of a severe iron deficiency that has progressed for some time, according to the University of Kentucky. Iron deficiency is also known as iron chlorosis. You can detect that a rhododendron has iron deficiency early if you know the first symptoms: The leaves of the rhododendron develop green leaf veins that have a whitish (chlorotic) or yellowish color between the veins, according to the University of Kentucky. If left untreated, the entire rhododendron shrub will eventually die. Iron deficiency can develop when soil pH is neutral or alkaline with a pH in the 6.5 to 7.0 range or higher.

Cultivation

• Rhododendrons thrive in partial shade, but they will tolerate shade. Therefore, they need a protected location with an eastern or northern exposure to avoid winter sunshine and winds that can dry the foliage. Avoid planting them too near the foundation of a building, because they might not get enough water there. Rhododendrons have a shallow root system. They also need a moist, well-drained, acidic soil with a pH of 5.0 to 6.5, according to Ohio State University. For best results, amend soil for the rhododendron with organic material such as leaf compost, aged manure, peat moss or topsoil.