Natural Needle Loss of Evergreens
Photographs courtesy of Rachelle Kreie
Is it a problem?
Needle loss in the fall is normal for many conifers. Even though these trees are called “evergreens” they do not retain every needle indefinitely. Many pines retain three to five years worth of needles and drop any needles that are older. The foxtail pine (Pinus aristata) usually retains eight to twelve-years worth of needles. Spruce and fir also drop their oldest needles each year.The oldest needles on a conifer are those closest to the trunk. Five years ago Rachelle’s trees put on a lot of growth. Those are the needles that can been seen yellowing in her photographs.
When conifers are under stress, they may shed their oldest needles several years earlier than normal, giving the tree a tufted appearance. Stress can be brought about by the lack of soil nitrogen, over-watering/soil compact and insect and mite pests. The misapplication of a pesticide can cause similar problems as can root damage. Root damage, however, often shows up as a spiral up and around the tree of reduced branch growth, yellow, browning and loss of needles and sometimes, branch death. (see the damage caused by root injury.)
Some conifers drop all of their needles in the fall no matter what you do. Bald cypress and larch trees are two of these deciduous conifers. The bald cypress at the Mesa County Arboretum turns golden each fall just before it drops its needles. This tree develops new needles each spring.
When an excessive number of needles are lost, tree growth can be negatively affected. Research in Finland by Kuirkela and Drenkhan concluded the three youngest sets of needles affect trunk diameter while the second and third needle sets affect the height of the tree. When 90% of the third-needle set (three-year old needles) were removed, height was 32% less and trunk diameter was 23% less than trees that had lost only ten percent of those needles. It therefore is important to maintain your trees in as healthy a condition as possible to ensure they lose no more needles than normal.
How to maintain tree health
Ensure your trees go into the winter in a moist condition, are watered each month this winter when snow doesn't cover the ground (Winter Watering Information, and fertilized with nitrogen after needle growth begins in the spring.
Needle-cast diseases do occur in some areas of Colorado but are very infrequent in the Grand Valley of Western Colorado. Needle cast fungal diseases affect the youngest needles while natural needle loss affects the oldest needles. To ensure your trees are not infested/infected with insect, mite or fungal problems you are welcome to bring a sample to our office at the Mesa County Fairgrounds for a free examination. If you want to email photos to our office they should be sent to Curtis.Swift@colostate.edu. We can also arrange to have a Master Gardener conduct a house call (Mesa, Delta, Montrose and Ouray Colorado Counties only) if you contact us at 970.244.1836. Leave a message and we will get back with you.
Placed on the Internet November 2, 2007
Updated on June 18, 2009