Fall Needle Drop: Evergreens are Not Forever
Conifers are highly valued evergreen trees that are aesthetically pleasing and add year-round color to the landscape. Every fall our phones ring with calls from concerned customers when they see the needles of their evergreens turn yellow, brown, or reddish in color, literally overnight. Most don’t realize that evergreens must drop their old needles at some point just like deciduous trees do every fall. Environmental conditions, transplant shock, diseases, and insects in conjunction with genetics determine the age when needles are shed. Often the natural shedding of needles goes unnoticed because new needles are produced every year, and thus there is a constant rotation between new growth needles and loss of old growth. Some evergreens shed their needles a few at a time while others have a more substantial seasonal shedding. Most pines can hold their needles for 2-5 years, while spruce trees generally hold onto their needles for 5-7 years. Concerns arise in years when needle drop occurs in a relatively short period of time, in contrast to years when browning is spread over a longer period. Natural needle loss in the interior or bottom of the tree is rarely a cause for concern but should always be checked by a professional. It occurs when the tree has become too dense or shaded by other plants or structures. This is a natural response triggered by the lack of sunlight penetrating the interior of the canopy. If the tree can no longer use the needle during photosynthesis to produce energy, it efficiently responds by shedding.
Keep in mind, evergreens do not replace the needles that drop and therefore this area of the tree will remain bare. In spring, new growth will occur at the terminal ends of branches. Natural fall needle drop may be more noticeable on trees that have experienced stress due to adverse growing conditions. Such factors include weather, climate, transplant shock, herbicide injury, pre-existing root damage, drought, and poorly drained or over-irrigated sites. It’s a common misconception that evergreens will live forever. Needle loss by evergreens will vary from year to year and between species due to inherent genetic differences and reactionary responses to site conditions. The challenge for tree owners and professionals is to observe these differences over time in order to identify what is typical and what is not. Needle loss that is abnormal is characterized by yellowing or dieback of new growth at the tips of branches or the exterior of the tree. Simply put, if the bulk of discoloration occurs near the buds, a more detailed assessment is warranted. It’s a good idea to have an inspection done by an ISA Certified Arborist of any suspect foliage to eliminate the possibility of disease, insects, or other potential causes such as winter injury (salt spray, desiccation), animals (feeding, urine), and even exhaust from vehicles/machines. Surprisingly, there are actually a few types of conifers that shed all their needles annually. These deciduous conifers include larch, bald cypress and dawn redwood. Such trees are unusual enough that many have been mistakenly removed by homeowners during dormancy because they were thought to be dead… Oops!!