Why Leaves Change Color

Fall leaves

Autumn, when the trees blush at the thought of stripping naked in public.”
– Robert Brault

Well, that’s a new way of thinking about fall leaves, isn’t it? In reality, the changing colors of leaves is a complex dance between reduced daylight, temperature shifts and moisture. These climactic factors trigger deciduous plants to prepare for  winter dormancy, with each species changing colors on its own timetable.

When temperatures begin to moderate and daylight decreases, it is a signal for plants to decrease and ultimately stop the production of chlorophyll, which in turn DSCN0428[1]triggers sugar storage in leaf cells, which is needed for winter survival. Chlorophyll is responsible for leaves’ green color, so in its absence, other pigments, which were always present are now “unmasked”. Two such pigments are carotenoids, responsible for the yellow in corn, carrots and  aspen and anthocyanins, which produce color in apples, strawberries and some maple trees.

Why are the fall colors more brilliant some years than others? Weather, both before and during the time chlorophyll production slows down, plays a key role, for example:

  • Long winters or  severe summer drought can delay fall color for a few weeks.
  • Moist fall weather and cooler temperatures keeps leaves bright and colorful longer.
  • Dry autumn conditions results in earlier loss of color, drying and dropping of leaves.

Parts of the Colorado  high country have been ablaze with golden aspen for a few weeks now, while other areas, including the Denver metro area, have yet to peak. The U.S. Forest Service offers a  Fall Color Hotline at 1-800-354-4595, while the map below shows typical time frames for various regions.


For more detailed information on fall leaves, be sure to check out:



Submitted by Linda McDonnell, Denver Country Master Gardener


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