Older White Pines Needles Yellowing in Fall
Many people know that deciduous trees, like maples and elms, lose their leaves every fall. But not as many know conifers also drop some of their needles in the fall. It’s a natural process that begins in the late summer and continues through the fall.
You may be alarmed when you start to see some needles on your white pine (Pinus strobus) or even your arborvitae (Thuja occidentalis) begin to turn yellow, then brown and eventually fall. How can you be sure that the browning is part of the tree’s natural processes or something else, like an insect or fungal disease?
The easiest way to be certain your conifer is healthy is to look closely at where the needles are browning. If the browning is taking place on interior needles while the outer most needles remain green then most likely everything is OK. Conifers routinely shed old needles. White pines drop two-year old needles while Colorado blue spruces (Picea pungens) shed needles that are anywhere from 7 – 10 years old.
If you’re still not sure if your conifer is healthy, you might want to check out this paper about conifer needle drop from Michigan State University Forestry Specialist Peter Kolb. It’s a bit technical but it does have some interesting photos and illustrations you may find helpful. Or visit your local Cooperative Extension website to see if they have any handouts for conifers specific to your region.
As long as the outer leaves are still green, then the yellowing of interior leaves is OK
By the way, broad-leaved evergreens,such as rhododendrons and Leucothoe, also drop old leaves in preparation for the cold winter. The same rule applies – if the yellowing leaves are located on the interior of the plant while the outer most leaves remain green, then the shrub is healthy and is just undergoing a natural process.
Fall will be must less stressful once you are sure your evergreen trees and shrubs are simply undergoing a natural process in preparation for winter just like your deciduous trees are doing. Too bad the conifers and broad-leaved evergreens don’t put on a more colorful show.
