Fall Foliage 101: Where and Why?

by Adam Paranich October 2022

The orchestra room has some of the largest windows in the school with the most breathtaking views. Everyday, all I can see behind the row of stands that sits in front of me is the beautiful yellow, orange, and red mirage that lays beyond the windows. Starting in September, the leaves began to transition from green to a slight brown color. Now, in the beginning of October about half of the leaves are green, and the other half are not. And by the end of October almost all leaves will be various colors. So why is this?

Leaves go through foliage. It all begins with photosynthesis. Chlorophyll is a key component present in all leaves. Its key attribute is its ability to turn sunlight into glucose, which then goes on to feed trees. As Chlorophyll cells have a green color, they make leaves appear green as well as they are so abundant.

Still, chlorophyll is not the only player in leaves. Carotenoids and anthocyanins are also compounds in leaves that play a big role in the game. And as fall days get shorter and shorter, chlorophyll production stops, leaving carotenoids and anthocyanins room to make more of an impact.

So let's talk about the common colors of leaves throughout the season. Yellow leaves are caused by flavonols. Flavonols are present in all leaves, but its impact isn’t always visible. Once fall comes, and chlorophyll production grinds to a halt, flavonols become a greater part of the leaf allowing its yellow color to show through.

Orange leaves are caused by beta-carotene. It’s one of the most common carotenoids present in almost all leaves. Since it absorbs blue and green light, it reflects yellow and red light from the sun, giving leaves their beautiful, vibrant orange hue.

Red leaves are caused by anthocyanins. Unlike the carotenoids, anthocyanin production increases dramatically during the Fall season. This protects the leaf, prolonging its life on the tree through the Fall season, and also provides the beautiful red hue to the leaf.

In terms of the geography of foliage, it begins in the north and affects the north the most. Starting around mid-September, foliage begins to have minimal effects in places like Montana, North Dakota, Michigan, New England, and other northern counties. Still, once you go to areas like Southern Pennsylvania, South Dakota, Oregon, and south of there, foliage stops.

Once you get to early-October, foliage begins to spread a lot. Areas like New England, The Upper Midwest, and other Northern States begin to reach their peak foliage. Areas like the Mid-Atlantic, the Lower Midwest, and the Upper Rockies begin to reach partial to near peak foliage. Still, some areas still have little to no foliage like Texas, the Deep South, and Florida.

Once you get to November, foliage will have affected every corner of the United States. Areas like New England and northern states will have already passed their peak. Areas like Pennsylvania, Lower-Midwest states, and Lower Rockies will have just reached their peak foliage. And even areas in the Deep South, Texas, and Florida will also be affected by partial foliage.

Overall, foliage is what makes fall, well fall. It creates a beautiful atmosphere that everyone enjoys. That's why Fall is America’s favorite season with 40% of Americans calling it their favorite season. The only bad part is frigid winters follow beautiful fall foliage.