The azalea falls into two broad categories: as the bright, small- to medium-sized evergreen shrub that is everybody’s favorite foundation plant; and as the more graceful and open deciduous shrub that tends to flower in relatively more subtle shades of yellow and orange. Some wild types of deciduous azalea have perfectly demure pink blossoms.
Closely related to rhododendrons (and botanically in the same genus), azaleas will grow in less than ideal conditions but are their healthiest and happiest in their preferred environment.
A typical shrub might be 6 feet high and 4 feet across after 10 years, but sizes vary significantly by type and age, and they take to pruning. Dwarf varieties are available that grow to just 12 to 18 inches.
Because of their potential for strong and clashing colors, including reds, magentas and rose-pink, they need to be used with care, in their placement and quantity. One problem with their use as foundation plants is their color tussle with the hues found in red brick. But set as a feature along a woodland path, the azalea can be a joyful expression of the spring garden. They are not resistant to deer.
Azaleas do best in areas of partial shade — in locations that are neither too shaded nor exposed to hot afternoon sunlight. They prefer soil that is organically enriched, moisture retentive and on the acidic side. It’s hardy in zones 5 to 8; colder for some varieties.
Most are container grown and can be planted in all but the hottest and coldest months. Take care to set the shrub at the same soil level as the container. After planting and watering, mulch lightly to keep the surface roots from drying out. For the first year after planting, keep plants watered as needed in periods of dryness and drought, but avoid constant soaking.
The surface roots should be lightly mulched in the spring and fed with a fertilizer formulated for acid-loving shrubs. In a hot, sunny location, a pest named lacebug is prone to suck much of the color out of the leaves. In such a spot, abelias or dwarf crape myrtles might be a better choice.
Countless hybrids have been developed over more than a century to instill hardiness to the large flowered Asian species, particularly the Glenn Dale hybrids developed in Maryland. (Their spring flowering at the U.S. National Arboretum is an annual event in Washington). A suite of azalea varieties that rebloom in the fall, branded Encore Azaleas, brings spring in October, if you want it.
For native-plant purists, several garden-worthy species are worth growing, notably the pinxterbloom azalea (Rhododendron periclymenoides), Florida flame azalea (R. austrinum), pinkshell azalea (R. vaseyi), coast azalea (R. atlanticum) and, for wet sites, the swamp azalea (R. viscosum).