From September through October, this yellowing or browning phenomenon shows as a change of color that starts from the inside out. It can be alarming to a gardener, especially if drought or pests have affected nearby shrubs and trees.
Though environmental stresses can certainly accelerate the process, seasonal shedding is normal and the rate of needle drop varies by species.
Needles generally begin dropping from the interior of a branch and an otherwise healthy conifer can look diseased if it still has brown needles clinging to its branches. It’s nothing to worry about—those brown needles will fall on their own.
These inner needles are also the oldest ones, and as they get shaded by new growth, they photosynthesize less efficiently and are eventually shed.
If you want to make sure your trees are indeed just dropping old needles and not new ones, take a closer look at the branches to see where the foliage starts to fade.