Autumn Leaf Color

nature · seasons · trees · science

Green hides the rainbow. All summer long, leaves are green because they're packed with chlorophyll, a chemical that helps trees make food from sunlight. When fall arrives and days get shorter, trees stop making chlorophyll, and the green fades away to reveal yellows, oranges, and reds that were there the whole time.

Only some trees do this. Deciduous trees, which lose their leaves in winter, put on the big color show. Evergreens like pine and spruce keep their needles green year-round because they don't need to shed them.

Different colors mean different things. Yellow and orange leaves contain xanthophyll and carotenoid pigments that were always there. Red and purple leaves are extra special because trees make these colors in fall, as if they're putting on a final show before winter.

It only lasts weeks. The whole autumn foliage season usually lasts just a few weeks, depending on temperature and weather. That's why people rush to see the colors before they fade to brown and fall off the branches.

Weather affects the show. Warm, sunny days and cool nights create the most brilliant colors. A frost or rainy weather can end the show early, so the best leaf-peeping years are when fall weather is just right.