Azaleas, classified under the genus Rhododendron, are popular flowering shrubs, but their foliage behavior varies significantly. The genus is divided into deciduous types, which lose all leaves annually, and evergreen types, which maintain some foliage year-round. This distinction is often confusing because evergreen azaleas do not behave like many other broadleaf evergreens. Understanding their specific leaf habits and hybrid groups is necessary for successful cultivation and selecting a plant that meets year-round landscaping needs.
Understanding Azalea Leaf Habits
The classification of an azalea as evergreen is based on dimorphism, where the plant produces two distinct sets of leaves. The first set, known as spring leaves, are relatively large, thinner, and appear early in the growing season, generally shedding in the autumn. The second set, or summer leaves, emerge later and are typically smaller, thicker, and more leathery in texture. These specialized summer leaves persist through the winter months, remaining on the plant for up to a year or more, giving the shrub its evergreen appearance. If exposed to extreme cold or harsh, drying winter winds, the plant may shed a significant portion of these persistent leaves to conserve moisture, resulting in a semi-evergreen habit.
Major Evergreen Azalea Groups
Southern Indica and Kurume Azaleas
The most widely grown evergreen azaleas belong to several major hybrid groups, many originating from species native to Japan and Eastern Asia. One recognizable group is the Southern Indica Azaleas, which are large, vigorous shrubs thriving in warmer climates (USDA Zones 8 to 10). These hybrids, such as ‘Formosa’ and ‘George L. Tabor,’ are known for their massive spring bloom and dense foliage retention in mild winters.
Another significant group is the Kurume Azaleas, which are smaller and more compact, typically reaching only two to four feet in height. Kurumes like ‘Hino-Crimson’ are valued for their extreme flower density and higher cold tolerance, often surviving in Zone 6 conditions.
Satsuki and Reblooming Hybrids
The Satsuki Hybrids represent a later-blooming group, known for their wide, often bi-colored flowers that appear in late spring and early summer. Satsuki varieties are characteristically low-growing and spreading, making them popular choices for groundcover or bonsai. Newer introductions, such as the Encore Azaleas, are unique for their ability to bloom repeatedly, offering a spring display followed by a second flush of flowers in the summer and fall. These hybrids were bred to be highly sun-tolerant and are considered evergreen, performing well from Zone 6 to 10. The Gable Hybrids, developed for greater cold resistance, are also popular, though some varieties lean toward a semi-evergreen habit, thinning out considerably in severe northern winters.
Maintaining Year-Round Foliage
Ensuring an evergreen azalea retains healthy foliage throughout the year requires attention to specific cultural practices. The primary threat during winter is desiccation, which occurs when leaves lose moisture faster than the roots can replenish it from frozen or dry soil. To combat this, provide supplemental water deeply and thoroughly in late fall before the ground freezes solid.
The shallow, fibrous root system of azaleas makes them vulnerable to drying winds and intense winter sun exposure. Strategically planting the shrub on the north or east side of a structure or beneath the canopy of deciduous trees provides protection. In areas with high wind exposure, temporary windbreaks, such as burlap screens, can shield the foliage from windburn and scorch.
Azaleas require consistently acidic, well-drained soil, with a pH range of 4.5 to 6.0 optimal for nutrient uptake. Applying organic mulch, such as pine needles or shredded bark, helps moderate soil temperature, conserve moisture, and protect the shallow roots from freeze-thaw cycles. Pruning should be minimal and performed immediately after the spring bloom to avoid removing next year’s flower buds.