Why do leaves change color in the fall?

October 27, 5:55 PMPittsburgh Gardening ExaminerTC Conner

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Autumn color in the country

 Fall has fallen, winter is on the way and we know it can't be stopped. Drive about an hour north of Pittsburgh, take any exit and you'll be here: The country.

When I was a boy growing up in Louisville, a river city much like Pittsburgh, my father would often take us to the country to visit his mother. We loved Grandma's house and I fondly remember the times my siblings and I would excitedly announce to each other: "We're goin to the country! We're goin to the country!" I-65 South from Louisville led to the country, the same kind of country I-79 North from Pittsburgh leads to.

And now, a short lesson in the science of why leaves change color.

Leaves are a tree's food source, taking energy from the sun through a process called photosynthesis (literally "putting together with light"), they turn water and carbon dioxide into glucose, a sugary substance that provides trees with the necessary energy they need to live and grow. Another chemical trees use to assist with photosynthesis is called chlorophyll, this is what gives leaves their green color throughout summer. The end of summer brings with it shorter and shorter days, and less sunlight, which means there's less glucose that leaves are "putting together with light." When this happens, trees know it's time to stop using energy and prepare for winter dormancy. This also causes chlorophyll to disappear from leaves, and we then begin to see the yellow and orange colors. Small amounts of color are present in the leaves throughout summer, we can't see these because they're hiding behind the green chlorophyll. The red and purple colors in the leaves of maple trees are caused by trapped glucose that is affected by lower fall temperatures and sunlight. 

Click here for more info on why leaves change color.

Visit Black&Decker for information on their 24V Cordless Mulching Mower (ideal for small to average sized lawns).

Please don't burn your leaves, or bag them for garbage pick up. Rake, pile, and allow leaves to decompose over the winter and then use as a natural soil amendment in spring.