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We have been fortunate the last couple of weeks with the amazing fall-like temperatures; which is not always the case in September for Central Alabama. If this temperature trend continues we are in for a season of beautiful fall foliage. You may be asking, “How do I know this?” and often I am asked “What are my prediction for the fall colors this year?” Well here's the answer you can share with anyone who asks.The cool mornings and changing of leaf color from green to shades of red, yellow,and orange can only mean that fall has arrived. We are primarily the only country in the world where the vast colors of fall leaves can be seen. People travel from all around the world to experience the changing of leaves to unbelievable colors in the eastern part of the United States. We truly are blessed to live right here in Alabama and have the opportunity to see the beauty of fall colors changing all around us.To explain making an accurate fall color prediction, let me remind you of the days in science class. The green color in leaves that we see all throughout the spring and summer is chlorophyll. Photosynthesis, the food-making process in the plant, takes place in the green, chlorophyll-containing leaves. As the day length changes and the amount of sun available to the leaves for photosynthesis begins to decrease, the living plant cells do not receive food and as a result, the leaves eventually die and fall to the ground.What about the colors? As daylight hours shorten and temperatures drop, chlorophyll breaks down and disappears allowing the yellow color (which has been there all along) to show through. The potential for the yellow color has always been there, just covered up by the green chlorophyll. So now you know that the leaves do not actually change colors bymagic; it's chemical processes in the plant that cause chlorophyll (the green color) to break down. So when someone asks you your projection for the fall colors this year, you can always say with certainty that it will be a great year for yellows!Now, what is it that brings along the amazing shades of red and orange that we all love to see in the fall of the year? While the process of photosynthesis is decreasing due to light changes causing yellow to appear, other chemical changes cause red, orange or even purple pigments to form. This is what gives plants such as dogwoods, sumacs, sweet gums, and other trees their red to purple fall colors. Sugar maples take on a fiery orange color, hickories will only show yellow colors, while oaks are primarily reddish brown to brown.So what triggers leaves to form the beautiful shades of red, orange, and even purple?.....warm sunny days with cool night temperatures, especially below 45 degrees. While we have not quite gotten down to 45 degrees, the nights in the 50’s are definitely a starting the process. These day and night temperatures extremes tend to raise the level of red coloration. The cool night temperatures trap the sugars produced during the warm sunny day inside the leaves.The interesting thing about fall color is that it can vary from tree to tree because of things such as genetics, physical location, or stress. Colors can even vary on the same tree. For example, leaves directly exposed to the sun may turn brilliant red while those on the shady side of the tree may only turn yellow. So now the mystery is solved and next time someone asks you for your projection for the fall foliage you can always say “The yellow fall color is guaranteed to be GREAT, but for the red, orange and purple foliage it will depend upon the the temperature swings.”
Mallory Kelley, ACES Home Grounds Regional Agent
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