Rhododendron and azalea

• Evergreen or deciduous
• Climate zones 4-6, 15-17, 34, 37 and 39 for best performance
• Light shade
• Regular watering

Both azaleas and rhododendrons belong to the same genus: Rhododendron. The group as a whole includes over 800 species, and countless cultivars have been developed from these.

These shrubs have exacting requirements. They prefer light shade or filtered sun (a good planting location is the area underneath high-branching trees). They need acid soil that’s well drained but constantly moist; to meet this need, you must either add large quantities of organic matter to planting beds or ― if the native soil can’t be adequately amended ― grow plants in containers. As a rule, they must have moist air and don’t thrive in hot, dry climates, though some handle such conditions better than others. They perform most consistently in the zones listed at left, but some cultivars and species also thrive in other areas; for best success, consult local nurseries or your Cooperative Extension Office for advice on rhododendrons and azaleas that do well in your region.

Deadhead shrubs after bloom to ensure a good flower show the next year. Individual stems may be cut back to main branches in late winter if plants are becoming too dense or too tall.

Rhododendrons. The most popular rhododendrons are medium to large evergreen shrubs with rounded clusters (trusses) of blooms in white and many shades of pink, red, purple, yellow, salmon, and peach. Elliptical, leathery, deep green leaves reach 5 inches or longer. Your selection will depend on your climate (some rhododendrons are hardier to cold than others), the flower color appropriate for your garden, and the plant’s ultimate size. The most widely available rhododendrons grow slowly to 6 to 8 feet high and wide, but you’ll also find choices in the 3-foot range. A common mistake is to plant a rhododendron too close to a house or walkway, where it soon outgrows the space.

Azaleas. The many azaleas include both evergreen and deciduous kinds; all of them typically bear small (1- to 2-inch), pointed-oval leaves. Deciduous sorts are typically showier than evergreen types, and they’re less particular about soil as well. They bear masses of blooms in shades of yellow, orange, and flame red; you’ll also find some bicolors. Fall foliage is often brilliantly striking, ranging from orange red to plain red to maroon.

Evergreen azaleas are an excellent choice where year-round greenery is wanted. Many do best in warmer climates, though new cultivars are extending the range. These plants offer a variety of sizes and flower colors. The smaller growers are often used as borders for shady pathways; they’re also popular as flowering gift plants (you’ll see these sold in nurseries, florists’ shops, and supermarkets).