Evergreens: Internal Needle Browning
Conifers that we call "evergreens" naturally drop their oldest, innermost needles each autumn. The age at which needle drop occurs varies between conifer species.
Needles of ponderosa pine last for 3-4 years and Austrian pine for 4-5 years. It could be expected that about 20-33% of the needles of ponderosa and Austrian pine would yellow, brown and drop each autumn. In years that evergreens have had good growing conditions, a larger amount of new growth and needles will occur. When the "drop-dead date" for needles on that above average growth arrives, it may appear that a greater proportion of the total number of needles is yellowing, browning and falling.
Keep in mind that occasionally, home landscapes may include a "deciduous conifer" such as baldcypress or larch. It is a normal event for these conifers to lose all their needles in the autumn, but a healthy tree replaces them the following spring.
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Updated Wednesday, October 12, 2016