“Why do leaves change color in the fall?”
If you’ve got a questioning child around, you may hear that often. But it’s not really a child’s question. Scientists have done much study on the question–and they still don’t have all the answers. However, they do have most of them.
As most people know, the green in our plants is caused by chlorophyll, which plants use to make manufacture sugars for their food by photosynthesis. What most people don’t know is that there are other pigments in many green leaves besides chlorophyll. These others are orange, yellow, and red (respectively).
During the growing season, new chlorophyll is constantly being produced as it breaks down–and the leaves stay green. When autumn comes around, the tree blocks off the connection between itself and the leaves, and chlorophyll production stops.
Once the chlorophyll breaks down, the other pigments have a chance to show their stuff. The orange and yellow pigments are produced (along with the green) all during growing season, but in the fall anthocyanins (the red) are manufactured from the sugars that are trapped in the leaf. And in plants where that happens, the others once again get masked, and you end up with reds and purples.
For the best red colors, it helps to have warm, sunny fall days and cool nights. You can find some trees where you’ll see red on areas that get a lot of warm sun and yellow on areas that don’t.