By Laurie Meyerpeter, Master Gardeners of Placer County
Q: Why did one of my trees turn color early this year?
A: Trees turn color for a variety of reasons. As the days shorten, they go through a number of stages leading to an explosion of red, gold, and orange colors of fall. Cool nights and warm afternoons produce maximum color. And each tree has a genetic code that predetermines what color it will turn and when it will begin.
A tree that turns color earlier than others in the neighborhood may just have a different genetic makeup. For example, Autumn Blaze maples turn earlier than Autumn Fantasy maples even though they are nearly identical. Autumn Blaze maples have a subtle genetic difference that causes them to turn earlier. All ginkgos turn later than all Autumn Blaze maples because that is what they are genetically programmed to do.
Or the tree might be growing in a slightly different environment than the others in the neighborhood. A tree growing in a low shady area gets a different amount of sunlight and may receive lower temperatures as the cold area moves down into the surrounding area. A tree growing on a sunny slope may receive more sun and warmer temperatures.
However, a tree that experienced some fall leaf color significantly earlier than normal was probably experiencing some stress. The most common stress that causes early fall color is lack of water. Often, the cause is not because a homeowner neglected to water it but that the tree experienced more heat or drought than it was accustomed to in the past. This past year has been a particularly dry year. Native oaks dropped leaves at alarming rates this summer as a normal reaction to the decreased moisture available in the soil as a result of the drought. Some native cottonwoods have turned yellow abnormally early in the season. Many other trees, particularly those growing in marginal areas, have also had early fall leaf color as a result of water stress.