Every year, evergreens experience a seasonal needle drop that is a normal part of the plant's cycle. Needles of conifers have varying life spans and do not remain attached indefinitely to the tree. Many evergreen needles, as they age, will turn yellow, then brown, and drop off after one to several years. The change can be gradual, or, with some species, quite rapid. Seasonal needle drop can cause concern to homeowners who are not familiar with this natural occurrence. In times of drought, needle browning may be particularly noticeable, because more needles are shed in response to environmental stress. White pines show the most dramatic needle drop change.
Their annual loss of needles can be especially alarming on mature white pines, as the number of yellow needles outnumbers the current season’s green growth. Typically, white pines will retain needles for three years, but in autumn, 2-or-3-year-old needles will change color and drop, leaving only the current season’s growth still attached. Austrian and Scots pines usually retain their needles for three years. Red pine drops its needles in the fourth year. Spruce and fir needles also turn yellow and drop, but the change is usually less noticeable because their older needles are thinned progressively, making the process more gradual than in pines.
Arborvitae sheds branchlets rather than needles which usually turn brown as they age, yet remain on the tree for quite some time before falling. Yew needles turn yellow and drop in late spring or early summer of their third year. Check your plants regularly. If the current season’s growth is discolored or wilted, the tree may be suffering from a more serious disease or insect problem and should be diagnosed to determine if control is warranted.
There is no control required. As long as needle drop is restricted to older growth and is not excessive, the “problem” is simply seasonal needle drop, a normal and natural process. Always follow good cultural practices to keep trees healthy.