Why do leaves change color?
Quick answer
Leaves change color in autumn because trees stop making chlorophyll, the green pigment used for photosynthesis, as days get shorter and cooler. As the green fades, yellow and orange pigments (carotenoids) that were there all along show through. Reds and purples come from new pigments called anthocyanins, made in autumn.
The pigments behind the colors
| Color | Pigment | Where it comes from |
|---|---|---|
| Green | Chlorophyll | Made all summer for photosynthesis; breaks down in autumn |
| Yellow and orange | Carotenoids (the same family that colors carrots) | Present all year, hidden by green |
| Red and purple | Anthocyanins | Newly made in autumn from sugars trapped in the leaf |
| Brown | Tannins | Left behind as the leaf dies |
Why trees do it
A tree can’t afford to keep leaves through winter in cold climates: water freezes, sunlight is weak, and leaves would lose water and get damaged. So the tree pulls valuable nutrients back into its branches and roots, then seals off each leaf at its base. Eventually the leaf drops.
Why some autumns are more colorful
The brightest displays usually follow:
- A warm, wet spring and a summer without drought
- Sunny, dry autumn days that let leaves make lots of sugar
- Cool nights (but not freezing), which trap sugar in the leaves and boost red anthocyanins
An early hard frost or a very rainy, cloudy autumn tends to dull the colors.
Which trees turn which colors?
- Red: red maples, sugar maples, sumac, sweetgum
- Orange: sugar maples, sassafras
- Yellow and gold: birch, aspen, hickory, ginkgo
- Brown: many oaks
Once the leaves fall, consider letting some stay where they land: here’s why you should leave fallen leaves in your yard. For another everyday color question, see why the sky is blue.
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