Why Do Leaves Change Colors?

I love the fall season. I love to watch the change in color of the warm-season native plants — forbs, grasses, trees, and shrubs. I’ve always known the change in color had something to do with the chlorophyll in the plants, but I thought it was about time I learned what happens to create the beautiful colors of fall. I knew it wasn’t magic.

The role of chlorophyll

I learned that the plants change color when they stop producing chlorophyll. Chlorophyll is the green substance in plants that interacts with sunlight throughout the warm seasons of spring and summer to make the food the plants need to grow, and gives plants their green color. This process is called photosynthesis, and it uses the energy from the sun to combine carbon dioxide and water into sugars.

The change to cooler weather, shorter days and less sunlight in the fall tells the plants to stop growing and to begin storing the sugars in their roots for next year’s growth. This reduction in chlorophyll lets other pigment colors in the plants begin to show. A steadier and more gentle temperature change from the warmth of summer to the cold of winter allows the fall color to change more slowly and linger longer. However, once we’ve had a freeze, the chlorophyll breaks down faster, and the plant colors will start changing quickly.

Once the leaves turn, the stem of the leaf develops a layer of cells and gradually severs the tissues that support the leaf. The tree seals the cut and the leaf blows away. Most trees in the north shed their leaves in the fall. However, leaves on the oaks and beeches will stay on the tree until the growing season starts up in the spring. The evergreen needles or scale-like leaves remain green year around.

What makes the brilliance?

I also found that weather conditions throughout the growing season and into the fall are what affect the brilliance of the colors we see. A drier summer typically means more vibrant colors, while a rainy summer typically means less vibrant, more drab colors. And a dry fall with more sunshine produces the deeper red colors.

   Send article as PDF