Why Do Leaves Change Color in the Fall?

When trees prepare for winter, they stop making food through a process called photosynthesis. During the warmer months, leaves are green because of a pigment called chlorophyll, which helps trees convert sunlight into energy. But when the days get shorter and cooler in the fall, trees stop producing chlorophyll, and the green fades away. That’s when we see the other pigments in the leaves.

• Yellow and Orange come from carotenoids, which are always in the leaves but hidden by the green chlorophyll.
• Red and Purple come from anthocyanins, which some trees produce in the fall to give leaves their bold, fiery colors.
• Brown is from tannins, which are part of the leaf’s structure.

When the green fades, these pigments become visible, creating the beautiful fall foliage we all love.

Leaves change color as trees prepare for winter, but why do they fall off? Trees shed their leaves to conserve energy during the cold months when sunlight is limited. Without enough light for photosynthesis, trees can’t make food, so they lose their leaves to survive the winter, growing fresh ones in the spring.

Want to learn more about why leaves change color in the fall? Here’s a fun and easy STEM experiment to try at home! You’ll use a simple technique called chromatography to see the hidden pigments in green leaves.

• A few green leaves
• Rubbing alcohol
• A coffee filter or paper towel
• A glass jar
• A spoon
• Plastic wrap
• A bowl of warm water

1. Collect green leaves from your yard or a park.
2. Tear the leaves into small pieces and place them in the jar.
3. Add rubbing alcohol to the jar until the leaf pieces are covered.
4. Mash the leaves with the spoon to help release their pigments.
5. Cover the jar with plastic wrap and place it in a bowl of warm water for about 30 minutes to an hour.
6. Cut a strip of coffee filter and dip one end into the liquid in the jar.
7. Watch the colors separate as the liquid travels up the filter, revealing the hidden pigments in the leaves!

This experiment works because of chromatography, a process that separates the different pigments in the leaves. As the liquid rises on the paper, you’ll see the green chlorophyll first, followed by yellows and oranges (carotenoids), and maybe even some reds (anthocyanins) if the tree produced them!