The Science Behind Autumn Leaf Colors

By Nina Walsh · October 3, 2026

Pigments That Create Fall Color

Autumn leaf color results from the interplay of three pigment classes as chlorophyll breaks down and other compounds become visible or are newly synthesized.

The Three Pigment Families

Carotenoids (yellow-orange): Always present but masked by green chlorophyll. Revealed as chlorophyll degrades. Found in ginkgo, birch, and aspen.
Anthocyanins (red-purple): Newly synthesized in fall from trapped sugars. Require bright light and cool nights. Found in maples, oaks, and dogwoods.
Tannins (brown): Waste products visible when all other pigments break down. Prominent in oaks and beeches.

Why Some Years Have Better Color

The best fall color comes from warm, sunny days followed by cool but not freezing nights. Drought causes early leaf drop. Excessive rain dilutes sugar concentration and mutes colors.

The Abscission Process

As days shorten, trees form a corky abscission layer at the base of each leaf stem. This blocks water and nutrient flow, trapping sugars and initiating color change.

Why Evergreens Stay Green

Conifers and broadleaf evergreens have waxy coatings and antifreeze compounds that prevent freezing damage. Their needles are built to last multiple seasons.