Azalea Adaptations

Azaleas thrive in the challenging habitats found in the Appalachian Mountains.

Azaleas are a type of rhododendron (Rhodendron spp.). In the United States, 17 different species of azalea grow natively, primarily in the mid-Atlantic and southeastern regions. Other azaleas originate in Asia, primarily Japan. Unlike rhododendrons, which keep their foliage throughout the year, native azaleas tend to lose their leaves in the fall, and their leaves feel thinner and softer to the touch. Azaleas are adapted to live in the acidic soils and mountainous habitats found in the regions where they grow.

Deciduous Foliage

The leaves of evergreen rhododendrons tend to feel thick and leathery to the touch. In the winter, when temperatures drop below freezing and plants can no longer extract water from the soil, the tough, waxy leaves of rhododendrons prevent water from evaporating from their leaves and keep the plants from drying out.

Azaleas, on the other hand, have soft, thin leaves that lose water more readily. In order to protect themselves from dehydration over the winter, azaleas follow the lead of many tree and shrub species in the temperate forest and shed their leaves in the fall when they go dormant. Energy stored in their roots powers the next spring's regrowth.

Soil Preferences

Most plants grow poorly in acidic soils. In the deciduous forest understory, however, where azaleas grow natively, fallen leaves and decaying plant matter keep the soil high in organic matter and with a low pH. In a 1993 study reported in the Journal of the American Rhododendron Society, researchers found azaleas in the Midwestern United States growing wild almost exclusively in rocky, acidic soils, indicating that these plants thrive in conditions found in the mountains that prove challenging to many other plant species.

Light Preferences

As shrubs that grow in a forest habitat, azaleas receive only the filtered light that passes between the leaves of the taller trees that surround them. For this reason, azaleas have evolved to grow best in areas where they receive only dappled sunlight, similar to that of the forests where they grow naturally. Full sun can damage their flowers, and heavy shade causes them to bloom less profusely. Azaleas also compete with trees for the water and nutrients that they extract from the soil with their roots. Their shallow, far-reaching root systems allow them to compete with trees that have much deeper, more extensive root systems.

Regeneration after Fire

The U.S. Forest Service reports that azalea species commonly found in mountainous eastern forests tend to regenerate easily after fire destroys the forest in which they live. The root crown of these azaleas survives the fire and gives rise to a new plant. Azaleas regenerate quickly after a fire, an adaptation that can provide important benefits for the plants, as they no longer need to compete for light with taller trees and can reestablish themselves before the forest canopy fills in again.

References

• Azalea Society of America: Azaleas
• Azalea Society of America: Native Azaleas
• Missouri Botanical Society: What's a Temperate Deciduous Forest Like?
• Journal of the American Rhododendron Society; Exploring the Deciduous Azaleas and Elepidote Rhododendrons of the Midwestern United States; Mark P. Widrlechner et al.; 1993
• U.S. Forest Service; Rhododendron periclymenoides; Milo Coladonato; 1992
• U.S. Forest Service; Rhododendron calendulaceum; Jennifer H. Carey; 1994

Resources

• Clemson Cooperative Extension; Azalea Care; Debbie Shaughnessy; Sept. 2000