Washington State University Extension

Garden Tips

Fall Color is a Treat

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written October 11, 2015

Fall is my favorite season of the year. Last week when I was in Spokane, I experienced exquisite tree and shrub fall color. What a treat! This change of leaf color from green to intense yellows, oranges, burgundy, and bright red has always been amazing to me. I can remember as a young girl collecting leaves each fall and my mother helping me iron them between two sheets of waxed paper. Did you ever do this?

Of course there is science behind this awesome transition. During the growing season most tree leaves are green. The green color in leaves is due to the green pigment chlorophyll. Also produced in the leaves are yellow (xanthophyl) and orange (carotene) pigments that are usually masked by the green chlorophyll. In the fall, as the days shorten and the weather cools, chlorophyll production slows and the chlorophyll already present starts to break down, revealing the underlying yellow and orange pigments.

What about red? Anthocyanins are the red to purple pigments in plant tissues. They are sometimes present during the growing season in plants with reddish to purple leaves, like red barberry or Crimson King maple. However, the red and purple pigments that show up in autumn are the result of anthocyanin production that starts as chlorophyll production slows and sugars in the leaf increase. Leaf sugar content and anthocyanin production is greater when sunny days and cool nights prevail, providing more intense fall colors and a more spectacular display.

Why do some trees like gingko and birch only have yellow and gold fall colors and others like red maple and scarlet oak have orange and red fall colors? While the amount and intensity of autumn leaf color is related to growing conditions and weather, the type of colors a tree is capable of producing depends on its genetic makeup.

What about trees that turn brown or copper in the fall? As just noted, some trees are not genetically programmed for fall color. Many types of oaks do not have a colorful fall display. This is because their leaves contain plant compounds called tannins. They are present all season long, but are also masked by chlorophyll. When the chlorophyll disappears, the brown tannins become visible.

Every fall I long for the beautiful autumn color display put on by the sugar maple forests of the northeast. Thankfully, that yearning has been assuaged a bit as more homeowners and municipalities have planted tree species that provide marvelous fall color.

Sugar maples do not thrive in our local climate but red maples do grow well and provide nice fall color. Two of my favorites are the red maples, especially Autumn Blaze with orange-red fall color and October Glory with orange to red color. You also can not beat the bright golden yellow of gingko trees like Autumn Gold, another one of my favorites for fall color. Add to that list Tiger Eyes sumac, American sweetgum, flowering dogwood, scarlet oak, and red oak.

If you want to plant a tree with great fall color, visit your favorite local nursery soon to pick a tree tree with the fall color that you like the best.

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