Leaves fall off an azalea either because of seasonal changes or because the plant is inconsistently watered or excessively fertilized. Deciduous azaleas normally drop their leaves in the fall, and leaves that drop in the summer usually indicate that the plant is in distress.
Deciduous azaleas shed their leaves each autumn, although dry weather sometimes causes the leaves to drop early, according to the Azalea Society of America. Evergreen azaleas produce two sets of leaves, one in the spring and one in the summer. The spring leaves grow near the base of the branches and drop in autumn. The summer leaves grow near the end of the branches, where they remain throughout the winter unless the plant is located in an extremely cold climate.