Rhododendron and azaleas are used as border foundational plantings with other shrubs. They create a mass of color when blooming and can be used in groups to create an effective background for other plants or as specimen plants. Their range of height makes them useful for tall backgrounds, medium hedges and low-growing borders. They are easy to transplant because they have a compact and shallow root system.
All rhododendrons and azaleas are classified as rhododendrons by botonists. Species are shrubs or trees and range in height from 4 inches to 98 feet tall. They are either evergreen or deciduous. The term azalea is commonly used for the smaller native deciduous species and some evergreen Oriental species. The name rhododendron is used for varieties that have large, evergreen, leathery leaves. The leaves are spiral shape ranging from under 1 inch to 19 inches.
Rhododendrons and azaleas thrive in moist, humid conditions and mild weather. They like the slightly acid soil provided by a mulch cover. The mulch should be renewed each year as it decays. A planting site on the north or east side of the house protects the flowering shrub from direct heat and wind. Filtered sunlight is considered the best condition for rhododendrons and azaleas.
There is little need for pruning azaleas and rhododendrons. When shrub growth is excessive it can be reduced with light pruning. The plant's shape can also be managed by pinching back new soft green growth. Picking faded flower blossoms on rhododendrons after the bloom phase is over encourages new bud growth. This practice is not necessary with azaleas.
Rhododendrons derived from the Catawaba hybrids have the greatest cold hardiness. Album grandiflorum has white flowers with lavender tinge that later fades to white. Astrosanguineum is very hardy and has red flowers with purple markings. America is a broad, bushy plant with bright red ball shaped flower clusters. Lady Armstrong is a rhododendron variety with deep purplish-pink flowers that have red markings.
There are azalea varieties for all USDA plant hardiness zones (please see Resource). Evergreen azaleas need protected sites. The most popular evergreens are the Kurume varieties such as Coral Bells, Pink Pearl and Snow. Deciduous varieties are cold hardy and provide a mass of color in the spring. Northern Lights, Korean, and Royal are popular hybrid varieties that bloom in a wide range of pastel shades.