Archive for Sunday, October 19, 2003

Weather has big influence on leaf color

October 19, 2003


Thankfully, the weather this fall has been ideal for the production of various leaf colors.

As a result, for past two weeks, sightseers have enjoyed a virtual painter's pallet of orange, red, yellow and purple. Without a doubt, one of the biggest joys of autumn is this variation in leaf color. If you are outside this weekend and enjoying the display, here are some answers to why leaves change colors in the fall.

The normal green color of plant foliage is produced by chlorophyll, which is the substance that captures energy form the sun and converts it into sugar and oxygen. Fall colors are produced by other pigments that begin to emerge when the green chlorophyll begins to break down. Reds and purples are caused by anthocyanins, yellows are due to the presence of xanthophylls and oranges are caused by a combination of carotenes and xanthophylls. Browns are the result of tannins present in the leaf. Most of these substances are present throughout the growing season but are masked by the green color produced by chlorophyll. Anthocyanins are the exception and are produced after the chlorophyll is destroyed in the fall.

Walnut trees are one of the first to turn colors and drop their leaves in the fall. They along with elms, soft maples and hickory turn yellow. Most ash leaves turn yellow, but some (such as autumn purple ash) have a purple cast. Red oak trees have brilliant red fall color, while white oak trees have a more subdued red color. Bur oak turn a buff to yellow color. Hard maples (such as those in Baldwin) have brilliant red hues.

Two plants that make an impressive display are sumac and Virginia creeper. Both have very bright red foliage. Sumac is often overlooked because it is a small tree confined to un-mowed pastures and tree-line edges. Virginia creeper is very spectacular when it grows up dead snags in the woods.

Weather has a major influence on fall leaf color. Warm, sunny days and cool nights are ideal for good color. The sunny days encourage photosynthesis and, thus, sugar accumulation in the leaves. As fall progresses, each leaf develops an abscission layer at the base of the petiole, or leaf stem, that prevents these sugars from being transported down the trunk to the roots for storage. This high sugar content in the leaves produces more intense colors. Cloudy days and warm nights prevent some of the sugar accumulation in the leaves and results in less vibrant colors. The length of time a tree maintains fall color also depends on weather.

Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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