Why Leaves Change Color in Fall: A Northern Virginia Guide

With so many picturesque places to view the changing fall colors in northern Virginia, the thought might have crossed your mind that you don’t actually know why leaves morph into these bright colors each year.

Get a refresher course on the scientific details of how and why leaves put on such a display each autumn and then impress your friends the next time you walk past a maroon-colored maple or a bright yellow birch tree (these are our five favorite trees for fall color).

Recipe For Vibrant Fall Colors

To achieve optimum fall vibrancy, certain elements are necessary.

• A spring and summer where trees received plenty of moisture and didn’t suffer from heat stress, diseases, or pests (drought or stress can cause the leaves to change color and/or drop early), and
• Cooler and darker fall nights with dry, warm, and sunny days (but without frost, which can cause an end to the fall foliage)

Leaf Color Change: The Scientific Formula

Leaves are mostly green throughout the spring and summer months, thanks to the chlorophyll that helps provide nutrients to the tree through a process called photosynthesis. As the days get shorter and the nights get longer, less sunlight hits the leaves, slowing the production of chlorophyll.

Without the presence of chlorophyll to block them, other pigments in leaves begin to show their colors. You’ll see the yellow, gold, and orange colors of xanthophyll and carotene on trees like birches and elm trees.

Bright sunny days followed by dark cool nights produce anthocyanins in trees like maples, dogwood, and sumac. These red and purple pigments are caused by a combination of chlorophyll, excess sugars in the leaves, and bright sunlight.

If the nights are warmer than usual, the colors will appear muted. But if the nights are cool and crisp (but not freezing), the colors will be bold and bright.

It Wouldn’t Be Fall Without Fallen Leaves

The longer nights also stimulate cells to grow where the leaf meets the stem. This is called the abscission layer, and as the cells build up, the connection between the stem and leaf grows weaker, eventually causing the leaf to fall to the ground.

Enjoy the Fall Leaf Colors

While trees might be a more popular attraction during the spring months (cherry blossom festival, anyone?), they are just as beautiful – and certainly more colorful – during the fall season. And you still have some time before it peaks – with the warmer summer and late fall weather that we’ve been having, colors aren’t expected to be at their most vibrant until November.