Needle drop is a term used to describe the normal process that happens to many evergreens during the fall season. While it is usually a normal occurrence it can be worrisome for homeowners not familiar with this seasonal change. Keep in mind that every needle on an evergreen has a certain life span. As it ages, the needle experiences a number of stages. This includes turning yellow, brown and eventually dropping off the plant. The length of time it takes the needle to experience all these stages will vary by evergreen species. Usually an individual needle lives from one to four years, with many being shed in the fall, causing a dramatic appearance all at once. White pine trees typically have the most drastic needle drop. Ordinarily, every fall the 2 or 3 year old needles will change color and drop, which leaves only the current season’s growth on the tree. The tree may appear sparse, until new growth starts the following season. Austrian and Scotch pines typically retain needles for 3 years. Other evergreen species, such as Spruce and Fir trees experience more gradual changes. The older needles fall at different times and not all at once. Even evergreens without needles experience seasonal changes. Arborvitae shed branchlets, rather than needles. The branchlets turn brown as they age, but remain on the tree for a long period of time before dropping. All evergreens will experience some type of needle or foliage change during their life.
Times of environmental stress may cause more needles to drop. This includes severe weather conditions, such as periods of drought. It is part of the plant’s protective mechanisms, which conserves moisture for the strongest and healthiest needles.
Yellow or brown needles and dropped needles are also symptoms of many insect and plant diseases that affect evergreens. It’s important to inspect plants carefully, to ensure they are experiencing a normal phenomenon and not more harmful issues.
To read more about this phenomenon in a past issue of the KTS Trunkline newsletter. You can also contact the Plant Health Care Department to have an Arborist visit your property for a thorough analysis. KTS provides trained Certified Arborists that can identify normal plant processes versus more serious conditions.