​

Why do leaves change color in the fall?

📓 The short answer

Leaves change color when chlorophyll (which we perceive as green) is replaced by other pigments, such as carotenoid and anthocyanin.

📚 The long answer

It’s hard to imagine autumn without colorful trees and crunchy piles of leaves. But why do leaves change color?

To answer that question, let’s start by understanding why spring leaves are green. The substance that makes leaves green is chlorophyll, a pigment that helps trees absorb sunlight and convert it into energy. This process is known as photosynthesis.

At the beginning of fall, the temperature drops and the nights get longer. This signals to trees that it’s almost winter and resources are becoming scarce. To conserve energy, trees stop producing chlorophyll, and the chlorophyll in their leaves begins to break down.

When the chlorophyll is depleted, other pigments in the leaves take center stage. Carotenoid pigments appear as yellow or orange, while anthocyanin pigments appear as red or purple. Without chlorophyll to mask them, these pigments cause the leaves to appear yellow, orange, or red.

Left: Close-up view of yellow carotenoid pigments from a persimmon rind. Right: Close-up view of purple anthocyanin pigments in an unidentified flower cell.

Left: "Кожура хурмы" by Andrei Savitsky is licensed under CC BY 4.0. Right: "Microscopic view of unidentified flower cells with anthocyanins (4x magnification)" by Shkyrik is licensed under CC BY-SA 4.0.

So why do leaves fall to the ground after they change color? Since chlorophyll produces the energy leaves need to stay alive, leaves slowly weaken without it. Throughout the fall season, they gradually separate from the tree until they fall to the ground.

While this process might seem sad, it’s a completely natural part of a leaf’s life. It’s actually a positive thing for nature as a whole! Rather than using up a tree’s much-needed energy, fallen leaves are able to serve as food for animals or fertilizer for the soil. Losing leaves also helps the tree survive through the chilly winter so it can sprout new leaves the next year.

📩 Subscribe to Madeline's newsletter

If you enjoyed today's post, I recommend you join Bluestocking, for more easy-to-understand breakdowns of science, history, and geography.

Bluestocking Learn fun facts with Madeline Have fun learning about history, science, and geography! Enjoy entertaining and informative videos, articles, and more created by a fun-fact-obsessed teen nerd (that’s me, Madeline). Subscribe to binge-learn every week! Subscribe​

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

​

📖 Book of the week

​The Elements of Style​ by William Strunk Jr.​ & ​E.B. White​

I've been trying to read more books on how to write better (for you, dear reader). This one is a must! I loved how this guide is concise and straight-to-the-point. There are plenty of examples to showcase okay writing vs. great writing, and I found myself noting down some key takeaways: "Omit needless words" will stay with me for life.

​
​Check out the full list of books I've recommended here.

👀 Catch up on other curious questions

• ​How do plants with purple leaves photosynthesize?​​
• ​Why does the wind blow?​​
• ​How do court reporters type so fast?​​

P.S. 🤔 Do you have a question for the newsletter? Click here to submit your question (or reply to this email!)