Some browning and needle loss is to be expected with all evergreens and is a natural and inevitable occurrence. In some cases, the browning and loss of needles may be due to injury and various forms of stress that can be corrected or at least controlled. In the autumn, evergreens shed some of their needles – a naturally occurring process that requires no remedial action. The needles that are shed annually are the older needles, those on the “inside” of the tree that are normally not seen because they are closer to the trunk and hidden by the outer foliage. This is a natural part of the aging process of the trees. When the needles reach a certain age, they turn brown and drop off. The life-span of needles depends of the type of tree. Pine trees shed needles that are 3 or 4 years old. The needles of spruce and fir trees brown and drop off at 5 or 6 years of age. This gradual needle shed from the inside of trees usually goes unnoticed because the needles at the outer parts of the branches normally remain healthy and green.
In the fall, evergreens will naturally have some of their needles brown and fall off. Pine needles age and are replaced by new needles, with a life span of about 3-6 years depending on the type of evergreen. This naturally happens to the needles on the inner part of the branches.
When the outer needles turn brown it is usually due to stress in the environment or injury of the tree. New needles will not grow where these needles have browned and died. The reasons for this can range, drought will cause needles to brown and fall as well as salt damage (salt in the soil, known by the yellowing of the needle first before it browns), insect damage, winter damage (when there is a particularly cold winter) and herbicide damage.
They don’t turn completely brown, but they do shed the foliage. As opposed to deciduous trees, it doesn’t happen all at once and there is no period when the tree is completely leafless. Leafs can persist for different times, from as little as few months to as much as few decades. This is why in a pine forest the floor is covered with dry needles that have been shed and replaced with new, green ones. It takes too many resources to regrow all of the tree’s foliage, and evergreens are generally growing on nutrient-poor soil. Gradual changing of leaves is much easier than a complete replacement.
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