Autumnal Equinox 2020: Why Do Leaves Change Colors in the Fall?

by Jon D. B.

Fall is finally here with the arrival of the Autumnal Equinox today. Weather perfect for outdoor activites and nature’s most spectacular display of color are just around the corner. But why does this display – the spectacle of leaves changing their color – happen only once a year?

While it may seem as though the leaves are gradually whithering before their eventual dying off -the science behind it is far more fascinating. Indeed, the biology of leaves is incredibly complex – and every bit as beautiful – as the foliage’s bright display.

To get the science just right, we’re pulling scientific facts straight from leading experts.

Autumnal Equinox brings fascinating biology into play

Close-up of red maple leaves in autumnal ornament. (Photo credit: Roberto Machado Noa via Getty Images)

One such expert is Ed Sharron, a science communication specialist with the National Park Service’s Northeast Temperate Network in Vermont. Sharron recently spoke with CNN on the very subject, breaking down the process. First up? Perhaps the most striking color change: natural green to vibrant red.

In short: the sugars vital to a leaves development begin to “bake” into a new pigment. As a result – we see lovely reds throughout Autumn.

The science behind red fall leaves

“The more favorable warm, sunny day/cool night temperature cycles that occur in early autumn, the more likely that fall season is to experience vibrant colors with lots of reds.

Leaves that get the most sunlight will develop red leaves, as the sugars inside them are “baked” into the red anthocyanin pigments. This is the same process that causes many apples to only be red on the side facing the sun as they grow.”

Ed Sharron

However, the glorious reds of fall are far from the season’s only color on display. Brilliant shades of ambers and orange, golds, yellows, and even purples are noted throughout.

So why do leaves, and other foliage, change to colors?