Maple-photo by Holly GuentherEvery year in fall something magical happens. Green trees that were unnoticeable before begin to draw the eye. The leaves transform into bursts of beautiful colors like gold, orange, red and purple.

How does this transformation happen? Well, let’s talk a bit about photosynthesis first. What exactly IS it? To get idea of what goes on inside the leaves of a tree, imagine you are one. A tall, stately tree “rooted” in one spot for the rest of your life. How will you eat? (ordering takeout is not an option) You’ll need to make your own food. To do this, plants use a process called photosynthesis:

Carbon Dioxide + Water + Light =Glucose (sugar) + Oxygen + Water

Plants use chlorophyll (a green pigment) to do their work to change CO2+H2O+light into sugar they can use. Plus, it just so happens that chlorophyll absorbs all the colors of the light spectrum except for green, which it reflects. This is why most plants are green!

Fall Color happens when the days become shorter and shorter,  and some trees (the *deciduous ones)”close down” for the winter and stop making chlorophyll. This pigment masked the other pigments of carotenoids (which cause yellow and orange) and anthocyanins (purples and reds).

So why does color vary from year to year? It has to do with the temperatures before and during fall, it can even go back as far as summer. The red and purple pigments are caused when days are sunny and cool and the evenings are cold but not freezing.  Cool nighttime temperatures prevent the sugars in the leaves from flowing towards the branches and the trunk (where they can be stored) and the anthocyanin pigments then “come to the rescue” to recover the nutrients before the leaves fall off the tree. Carotenoids, which cause yellow and orange are fairly constant and do not vary much from year to year.

So when October rolls around, remember to stop, take a look around and enjoy! Get out of your car and walk around, the colors may last until early December, but you never know when that last leaf will drop.

*deciduous trees (like maples, birches or crape myrtles) lose their leaves all at once, while evergreen trees (like pines, firs and bay laurel) lose their leaves a little each day