Most everyone likes the change to cooler weather, football season, and the colors that come with it. But what makes trees change colors and what determines whether we will have a good season of fall color or not?
There are 3 main factors that determine fall color: sugars/pigments in the tree, weather, and length of day.
Pigments – every tree and plant have sugars and pigments. Cholorophyll, Carotenoid, and Xanthophyll are all of the yellow/green sugars and pigmentations. The yellow pigmentations are almost always present, all year long, but are masked by cholorphyll, which gives trees and shrubs their green pigmentation. Anthocyanin is the red pigmentation found in some trees more so than in others.
Weather – bright sunny days, with cool, crisp nights are needed to help slow the production of cholorphyll and help convert other sugars into Anthocynanin to produce red coloring. A good supply of moisture is also needed, but its hard to get moisture in the fall and have bright sunny days. So, its better if the moisture comes in the spring and summer and a little throughout the fall, allowing for the warm sunny days in the fall.
Length of Day – probably the single biggest factor that begins the process of leaves changing colors. As the length of day shortens, nights get longer and cooler, the making and storing of sugars begins to change and unveils various colors.
So, just about every year, you should see good yellow coloring in trees because it is always there and is just masked by the green Cholorphyll. As the Cholorphyll production slows and then stops, the yellow coloring comes to the forefront. But for good orange/red fall color, we need a good moisture supply throughout spring and summer, and shorter days and cooler nights (upper 30’s to upper 40’s) for trees with red pigmentation to begin producing it. This is why changes obviously occur farther north first. Additionally, various species of trees produce varying amounts of each pigmentation and change at slighlty various times.
Did you know that the best fall color occurs primarily along the middle and eastern part of US/North America, small portions of Europe, and Australia? (as always exceptions apply)
Resource: check out this site as you plan your fall trip to the mountains to see when the peak color change may be.