Fall is most closely associated with leaves dropping form deciduous trees, like oaks and maples. But did you know that evergreen trees, such as pines, shed their needles also?
"Evergreen" does not really mean that the trees stay green for the entire life of the tree. It actually means that the leaves or needles stay green and attached to the plant for more than one year. Most evergreen leaves grow two to three years before shedding.
White pines and arborvitaes will drop their needles in the fall after two years. Some species of juniper can keep their needles for 10 years or more. Broadleaf evergreens, such as hollies and magnolias, shed their older leaves in spring as new growth begins.
Pines still shed needles for several reasons. The older needles become worn out and lose their productive efficiency. The may also become shaded out by the younger, more vigorous needles produced in the spring. Because there is a natural growth and shed cycle, shedding needles are replaced with newer needles every year. The old needles fall to the ground and become pine straw which helps retain soil moisture around the tree.
Now is the time when you will most likely see some brown needles on your pine trees, especially white pines. If you examine your trees closely, you will notice that most of the discolored needles are located on the inner sections of the pine branches. Needles on the outer portion of the branches should remain green. This phenomenon is completely normal and does not mean the tree is in any danger of dying.
Environmental stress, such as drought or over-watering, throughout the year will intensify needle drop in the fall. If your pine tree is showing discolored needles on an entire branch or is brown throughout the entire tree, insect or disease damage could be the culprit.
Other factors may contribute to evergreen needle drop throughout the year. Nitrogen deficiency will show up in a pine with similar symptoms as natural needle drop. Plants can move nitrogen from older to younger leaves to protect the new growth. This will cause the older needles to discolor and drop.
Waterlogged or extremely dry soils, insect injury, disease, air pollution, and chemical injury can also cause needle drop symptoms.
Rest assured that fall needle drop is a natural condition and doesn't affect the health of the tree. Enjoy witnessing the plant life cycle at work as the seasons change. And enjoy the free pine straw.