The common rhododendron (Rhododendron spp.) is an evergreen shrub with leathery leaves and showy flowers. Rhododendrons, which belong to a genus with more than 850 species, come in a variety of sizes and shapes, with flower colors that span the rainbow. They are native to most of the world's temperate areas, with the majority originally coming from Asia.
Rhododendrons are a diverse group of shrubs. Their leaves can range in size from 1/4 inch to 3 feet long, and can be elliptical, lance-shaped or rounded, according to the Rhododendron Species Foundation. Flower colors include red, pink, magenta, orange, yellow, purple and white, with all shades in between and sometimes in mixtures. Rhododendrons generally bloom in early spring, though some varieties may flower in January or as late as August.
Rhododendrons are often used as foundation plantings, in woodland settings under tall oak trees or pines, as specimen plants, espaliered against a trellis, or even in containers. Oaks and pines give these shade-loving shrubs a high canopy of filtered shade with just enough light, according to the Rhododendron Species Foundation.
Soil and Location
Well-drained soil is vital to growing healthy rhododendrons. The ideal location for the shrubs is on a slope with northern exposure. The shrubs should be planted out of the wind and in light shade. Direct sun will scorch their leaves. Rhododendrons prefer a soil pH between 5.0 and 5.5. Soil that is too alkaline can be amended with ammonium sulfate, but always test your soil before applying. Mulching with pine needles not only helps retain moisture and improve the soil, but adds more acidity.
Water and Fertilization
According to Clemson Extension, rhododendrons have shallow roots and need to be watered consistently during dry periods. You may need to regularly water newly planted shrubs during dry spells for the first several years after planting, particularly if the soil is sandy. Over-watering can lead to root rot diseases, which is why well-drained soil is so vital.
Once established, rhododendrons need very little fertilizer. Newly planted shrubs can be fed after several months with a complete fertilizer such as 12-4-8 or 15-5-15, according to Clemson Extension.
Pests and Diseases
Good cultural practices, adequate nutrients and well-chosen planting sites will keep pests to a minimum for your rhododendrons. The most common pests are mites, scale, lace bugs and borers. Diseases that affect rhododendrons include scorch, sunscald and iron chlorosis. Regular watering, correct light conditions and an acidic pH in the soil should help avoid most diseases.