What are the Best Conditions for Brilliant Fall Colors?

Also important in the quality of a leaf color season is another chemical in leaves called auxin. Auxin controls a special band of cells at the base of each leaf stem, called the abscission (cutting away) layer. During the growing season, auxin prevents this layer from fully developing and blocking the tiny, internal tubes that connect each leaf to the rest of the tree's circulatory system. 

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In fall, however, cooler and shorter days trigger an end to auxin production, allowing the abscission layer to grow and cut off the circulation of water, nutrients and sugar to the leaves. When this happens, chlorophyll disintegrates rapidly, letting carotenoids shine through as yellow and the anthocyanins as red. The color season ends when the abscission layer finally cuts the stem completely, and the leaf falls off. 

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Tree Types and Color
Certain colors are characteristic of particular species. Oaks turn red, brown, or russet. In fact, in the absence of yellow or red pigments, oaks turn brownish due to another pigment–tannin. Hickories turn a deep golden bronze whereas aspen and yellow-poplar are golden yellow. Dogwood will turn purplish red and beech light tan. Sourwood and black tupelo are crimson. Maples differ according to species. Red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel up and fall off, exhibiting little color other than drab brown.

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Best Conditions for Brilliant Fall Colors
Putting together all we’ve learned, what is the optimum scenario for a brilliant fall? The best weather for brilliant fall foliage is a growing season with ample moisture followed by a dry, cool and sunny autumn with warm days and cool but frostless nights. On the other hand, cloudy days, an early frost, strong winds, or heavy rains can all reduce the quality and length of the color season. In time, regardless of conditions, the brilliant leaves of autumn fade and fall to the ground. 

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Which brings us to one last tidbit–why the season is called “fall.” The word fall comes from an Old English word feallan which means "to fall or to die.” The "fall of the leaf" was used to refer to the third season of the year when trees lost their leaves, but over time, the phrase was shortened to fall. Regardless of what we call the season, it’s a glorious time of year. Let’s hope the conditions are right this year for a brilliant fall!

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