October 7, 2012

How and why leaves change color


Besides chlorophyll, leaves contain pigments, such as carotene, which gives carrots their orange color. Without the presence of chlorophyll, the yellow and orange pigmentation becomes visible. At the same time, sugars that become trapped in the leaves of certain trees, such as sugar maples, react with sunlight and other acidic leaf chemicals, producing radiant reds and purples.

Temperature, light and available water all affect the intensity and the length of the color season. For example, prolonged temperatures just above freezing will result in sugar maples turning bright red, but an early frost may cause colors to appear faded or dull. Timely rains may cause colors to become more intense.

Trees eventually form a layer of cell tissue at every point of leaf stem attachment, effectively severing the leaves from the limbs. When a leaf falls from a tree, a small scar remains.

Do evergreens like pine, spruce and balsam fir lose their leaves as well? The answer is yes. These conifers do shed their needles in the fall; not all of their needles, just the oldest, less-healthy ones. The younger needles remain on the trees all winter.

Richard L. Gast, Extension program educator II, Horticulture, Natural Resources, Energy, agriculture programs assistant, Cornell Cooperative Extension of Franklin County, 355 West Main St., Suite 150, Malone, 12953. Phone 483-7403, fax 483-6214 or email 

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