Why do leaves change color in the fall? Why is fall color better in some years than others?
Green leaves actually contain colorful pigments all season, but during the growing season those colors are masked by an abundance of green chlorophyll. Chlorophyll is used in photosynthesis, the process in which the tree uses sunlight to produce food. The shorter fall days signal to the trees that winter is coming and it will soon be time to shed its leaves. At this time the tree stops producing Chlorophyll and the colorful pigments that have been there all along are finally revealed.
The brilliance of fall color is affected mostly by the sunlight; however, temperature fluctuation and soil moisture also play a role. A series of warm sunny days, followed by cold, but not freezing night time temperatures will produce the best fall color. If the trees experience a fall with a lot of cloud cover and moderate temperatures, the color will be dull. In addition, a wet spring followed by a moderate to dry summer and fall will produce the best fall color. During late summer and early fall, if a tree is under a slight amount of stress due to dry soil conditions, it will have more brilliant color.
If you are interested in finding out more about the science behind tree color in the fall, visit the following link from the UNL extension office.