In the Garden:
Western Mountains and High Plains
October, 2012
Regional Report

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This 60-year-old blue spruce eventually sheds its inside needles.

Evergreens Shed Their Leaves Too

It's been a colorful show from the deciduous trees and shrubs, and now the leaves are falling. But have you noticed your evergreens lately? The 60-year-old spruce at the old farmstead is displaying subtle changes, too. There's a distinctive browning showing towards the inside of this majestic tree.

Despite their "evergreen"name, conifers like Colorado blue spruce, firs, and pines eventually lose their needled leaves, too -- just not all their needles at the same time, the way deciduous trees lose their leaves each fall. The various kinds of evergreens in your landscape may be going through this process of needle shed now. It depends upon the age of the tree. Some pines, like the Eastern white pine, keep their needles for one year, dropping the previous season's needles the following fall. The bristlecone or foxtail pines, in contrast, keep their needles for up to eight years. So it takes this pine eight years to show signs of shedding the oldest needles.

The Austrian, mugo, and pinyon pines hold on to their needles for two to four years. The browning or needle shed starts during that maturation period and shows itself towards the inside of the tree.

Colorado and blue spruces, firs, and Douglas fir are in different conifer group and their needles are not arranged in clusters like those of pines. They generally hold on to their needles much longer than pines do. But they, too, will eventually lose their older needles. In older and denser spruces, you can often observe a yellowing that turns to brown on the inside closest to the trunk.

When you see needles begin to yellow and fall, it's important not to jump to the conclusion that your evergreens are diseased or infested with bugs. And don't assume that the trees need more water. Adding too much water in clay soils tends to reduce the amount of oxygen reaching the roots and leads to serious problems.

So take a closer look at your evergreen trees this fall. If the needles are dropping off from the inside out, that is, the needles that are closest to the trunk of the tree, this is a natural phenomenon. The time to become really concerned with browning is when it shows up on the current season's growth or shows up over the entire plant.

If you do see signs of stress unrelated to the natural cycle of needle drop on your pines, firs, and spruces, lightly cultivate or core aerate around the dripline of the trees. This leaves the soil more permeable to fall and winter moisture and reduces soil compaction.

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