Learn / Ask The Landscape Professional
Why do leaves turn colors in the fall?
Answer
Shorter days play the major role in the changing
leaf colors of autumn as well as cooler temperatures
and the pH of the soil.
Believe it or not, leaves are always shades of
yellow; you just can't see the colors during the
summer! Trees are amazing living things. They
take water from the ground, carbon dioxide from
the air and sunlight to produce oxygen and food
(sugars). The process of converting sunlight
into energy that the tree can use is called Photosynthesis.
A critical part of the Photosynthesis
process is the absorption of sunlight through
the leaves which regulates the production of the
green pigment called Chlorophyll. In the summer, leaves appear green because green is the
dominant pigment, obscuring other pigments in the leaves. As the days get shorter in the fall,
less Chlorophyll is produced due to the reduction of light, and the trees begin to go dormant. As
Photosynthesis comes to an end, the green Chlorophyll fades from the leaves unmasking the
shades of yellow pigments that were present all along. The yellow pigments are called Carotenoids.
Another process that happens at the same time is a corklike layer at the base of each leaf forms
causing the leaf to detach from the tree. But before the leaves fall off, the tree "senesces" or
transfers its (sugar) energy out of the leaves into the roots. This higher sugar concentration
creates the production of red pigments called Anthocyanins. The red color of the Anthocyanins
actually protects the leaf cells from sunight damage while they are senescing. The leaves
of some trees, like birches, will turn yellow (because of the high quantity of Carotinoids within
its leaves), but not red because birches are much more tolerant of sunlight and don't need the
protection offered by the Anthocyanins. A Sugar Maple appears orange because of the combination
of Anthocyanins and Carotenoids within its leaves. A Blueberry shrub with its bright red
leaves has Anthocyanins as its dominant pigment.
One of the best things about autumn is that each year is different because the pigments that are
visible are affected by the weather. Bright, sunny and cool autumn days produce the most colorful
foliage displays of oranges and reds. If the weather is overall dry and overcast more yellows
and browns will dominate the color palette.
Enjoy the fall colors!
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About Linda Lillie
Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier
landscape design and maintenance, tree care, lawn care, stonework, and carpentry
service provider in southeastern Connecticut since 1997. She is a graduate of
Connecticut College in Botany, a Connecticut Master Gardener and a national
award winning landscape designer for her landscape design and landscape installation work.
