Fall Foliage: Why Leaves change color

Fall is without doubt my favorite time of the year. As a gardener you may be considering planting trees for beauty and sustainability. If you are thinking about planting deciduous trees, fall color is one factor you might want to consider.

Here it is late September and it won't be long before the fall leaves color the mountains with vibrant tones of red, yellow and green. You can even be given fall color alerts through the various national weather channels!

Colors usually peak around the last half of October with the higher elevations changing color first and then trickling down into the valleys.

If you have a child, you've probably been asked why trees leaves turn yellow, orange, or red in fall. Although you might not think of it as a color, brown is another color of fall. You have to understand a little about botany to get a better grasp on fall colors.

As the chlorophyll breaks down in the leaves, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. The autumn foliage of some trees show only yellow colors such as our local poplars here in the Pacific Northwest.

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn months, one or many colors that range from red to yellow. Autumn colors (especially red) are not just due to the breakdown of chlorophyll; in fact anthocyanins (red-purple) are actively produced in autumn. Autumn weather conditions favoring the most brilliant colors are warm sunny days and cool, but not freezing, nights. The amount of rain in a year also affects autumn leaf color. A warm, wet period during fall will lower the intensity, or brightness, of autumn colors. As sunlight decreases in autumn, the veins that carry sap into and out of a leaf gradually close. The brightest colors are seen when late summer is dry, and autumn has bright sunny days and cool (low 40's Fahrenheit) nights.

Now this is interesting: University of Wisconsin-Madison scientists have a new theory about why autumn leaves turn scarlet and why the hues are more vibrant some years than others. They say that the red pigments -- called anthocyanins -- in plants such as maples, oaks, dogwoods and viburnums act like sunscreen. "The pigments shade sensitive photosynthetic tissue in fall while trees reabsorb nutrients from their leaves," says horticulturist Bill Hoch. "Trees need to store as many of those nutrients as they can before the leaves drop."

Here is my interpretation of Autumn: Autumn is warm lazy days with crisp nights whispering of the winter to come. The days are shorter and our gardens are shutting down for a long winter's nap. Even human beings respond to the changing season. Fall weather signals us to get our crock pots out and make wonderful steamy soups and stews. I love autumn!

The way leaves change color is, in its own way, no less miraculous, the result of a complex shift in chemistry as a tree prepares itself for its winter dormant period. Through fallen leaves, Nature has provided the decaying leaves to help replenish and add to the fertile forest floor. And the cycle of life goes on!