Defoliating Azaleas and Hollies?
That means you forgot to feed them
Are your azalea leaves yellowing and dropping? The loss is more than winter’s toll. You could have prevented it if you had mulched your azaleas with one or two inches of compost in early to mid-September or applied one-quarter cup of an ammonium-based fertilizer soon after the first frost.
Lacking that help, nitrogen is now translocating from the older leaves to the flower and vegetative buds at the ends of the branches. During late fall and winter, buds are enlarging in preparation for spring when the flower buds open and vegetative buds produce new stems. If the roots of plants cannot provide sufficient nitrogen to the ends of the branches after the plants have stopped growing in the fall, nitrogen from the older leaves will migrate out of these leaves and move up the stem to where terminal flower and vegetative buds develop. Nitrogen is the only plant nutrient that can move about after its initial distribution when plants were in active growth. The translocation of nitrogen is most active in the fall when temperatures are above freezing.
The leaves of white-flowered azaleas yellow before falling. The leaves of red- and pink-flowered azaleas generally turn red to purple-red just prior to leaf drop.
This same problem occurs with American holly, especially female hollies that produce an abundance of berries. The production of holly berries requires an abundance of nitrogen. If the roots cannot supply the nitrogen needed, buds will rob the nutrient from the leaves. However, with hollies, the nitrogen is translocated rather uniformly from all of the existing leaves, which causes the uniform yellowing of the foliage. Under severe nitrogen-stress, hollies will drop leaves extensively.