Why do leaves change colors in the fall?

By Casey Frye, CCNN Writer

purple leaves
These are the purple leaves of a Norway Maple.

Ah, the fall season is nearly at an end, with winter right around the corner on December 21. That means really breezy days and orange leaves riding the wind like a cowboy. Oh, and let’s not forget all the crunchy yellow, red, and brown ones too! Hmm, you ever wonder why leaves are green throughout most of the year, then change colors in the fall?

The answer has to do with chlorophyll, which is a chemical inside leaves that not only drinks sunlight for energy, it turns them green. However, another colorful type of chemical, carotenoids, also swims around inside our leafy friends. You might be interested to know that it’s these carotenoids who are responsible for bananas being yellow, yams being brown, and carrots being orange!

As if that didn’t cause enough of a plant identity crisis, leaves also have chemicals called anthocyanins, which give blueberries and strawberries their blueish-purple and red hues.

Even though chlorophyll, carotenoids, and anthocyanins are all found inside leaves, chlorophyll overpowers the other two pigments (color-affecting materials) when it comes to choosing what shades the leaves wear. However, just like our skin cells are constantly broken down by the sun and replaced, leaves have to change out their chlorophyll. This process happens to use a lot of energy!

So, when autumn comes along with its reduced sunlight, chlorophyll takes a backseat as it begins fading away. Because trees know how tough winter can be, they decide that keeping all those leaves healthy just isn’t worth the energy. After all, they need to start storing up their power to survive the frosty darkness. As the chlorophyll finally withers away, carotenoids and anthocyanins get the chance to show their true colors, hence the yellow, red, orange, brown, and sometimes purple leaves!

Featured image courtesy of CR Artist on Flickr. Image of purple leaves courtesy of Matthieu Sontag on Wikipedia.