You may have noticed your evergreen shrubs and trees shedding yellow and brown leaves this spring. It seems unusual, but it could be a normal leaf and needle drop. While some may believe that evergreen leaves last forever, the truth is that their leaves may only last for a short time, often between one to a few years. Sometimes normal leaf drop goes unnoticed in the fall, for example, with pines and azaleas, because it coincides with the normal shedding of leaves in deciduous plants. As the dormant deciduous plants leaf out in the spring, it seems unnatural for hollies, live oaks, and magnolias to lose their leaves. Is this a distress call for help? Not necessarily.
Evergreens normally shed their oldest leaves and needles, which are closer to the trunk than the newly emerged younger leaves at the ends of branches. Like car tires that need to be replaced after several thousands of miles, the plant will replace these older, compromised leaves naturally.
As the older leaves turn from green to yellow, red, or brown, some of their contents, notably nitrogen and phosphorus, get recycled back into the plant. With normal leaf drop, the new young leaves at the ends of the branches appear healthy and green. This out-with-the-old-and-in-with-the-new growth stage may occur over several days to several weeks.
Not all leaf-shedding is normal, especially when the new growth is affected or when all of the leaves turn yellow or brown. Drought or injury from voles, insects, or diseases also cause leaf drop. In addition, low soil fertility, waterlogged soils, or a high soil pH can turn the leaves yellow.
For more information, see HGIC 2353, Leaf & Needle Drop.