Why Leaves Change Colour – Fall Leaf Science Explained

When the days shorten and the air turns cooler, trees begin a transformation you can see all around you. Leaves change colour in autumn because trees shut down their food-making factories. During spring and summer, leaves fill up with chlorophyll, a pigment that captures sunlight and gives leaves their green colour. As daylight fades and temperatures drop, trees stop producing new chlorophyll, and the green begins to fade.

Uncovering Hidden Pigments: Carotenoids

Carotenoids—yellow and orange pigments—are present in leaves all year long, but in summer they’re hidden by the dominant green of chlorophyll. When chlorophyll breaks down in fall, these carotenoids are finally revealed, giving leaves their golden and amber tones.

Sugar, Light, and the Creation of Red: Anthocyanins

The bright reds and purples come from a pigment called anthocyanin. Unlike carotenoids, anthocyanins are produced in the fall after chlorophyll declines. They form when sugars left in the leaves react under light and cool nighttime temperatures. Trees that trap more sugar in their leaves often show stronger reds.

How Weather Affects the Colours You See

Autumn weather plays a big role in how bright or muted the leaf colours look. Warm, sunny days and cool (but not freezing) nights favour stronger reds and purples. Too much rain, early frosts, or cloudy days can dull the colours or make leaves drop early.

Leaf Drop

After the colour show, the trees prepare to let go. A special layer of cells forms at the base of the leaf stem, separating the leaf from the tree. Once that “abscission layer” finishes its job, the leaf falls away. The tree reclaims as many nutrients as possible before the leaf drops. Bringing It to The Hook Book Barrel

In our latest episode, we explain all this using real leaves and simple visuals—and then we settle in to read Valley the Wiggle-Butt Pup by Jae Lynn. If you want a fun, kid-friendly way to see this fall science in action, CHECK OUT THE EPISODE!