Dallas Morning News - October 21, 2021
Fall Color
It's fall and there's a nip in the air. Besides time spent on football, school activities and holidays approaching, it's time to enjoy a little fall color from our trees before full fledged leaf management kicks into gear and I have to continue to remind homeowners and businesses to mulch the leaves rather than send them to the landfill.
What causes and controls fall color anyway – temperature, soil moisture, shorter days, sunny days? All of those factors actually, but here's what technically happens.
Green chlorophyll is present in leaves in large quantities during the growing season. As the days shorten, chlorophyll production slows to a stop.
 Texas ash fall color ranges from bright yellow to deep reds all on the tree at the same time |
As chlorophyll breaks down in the leaves, two compounds called anthocyanins and carotenoids take over. Carotenoids are leaf pigments responsible for yellow and orange colors. They are present in leaves during the growing season but masked by the green chlorophyll, except in plants that are stressed or with naturally yellow leaves. Carotenoids are helpful in that they absorb wavelengths of light that chlorophyll doesn't accept - mainly blue-green and green. They also use excess energy produced in leaves as happens in high light conditions. In fall, with no chlorophyll left, they can act as a sunscreen to help protect foliage.
 Prairie or flame leaf sumac has spectacular red fall color |
Anthocyanins are pigments responsible for red and purple fall leaf colors. These compounds are only produced in the fall when sugars are trapped in the leaves. They function similar to carotenoids to help leaves use up remaining energy as chlorophyll disappears. Dry weather and sunlight lead to more sugars in leaves, which leads to brighter fall reds. More red in leaves, and earlier reds can sometimes result from plant stresses due to low nutrition, near but not freezing temperatures and root flares being covered with plants, soil, and mulches.
Hard freezing stops the process of pigment creation and as colder weather moves in, even these colored pigments break down, leaving behind brown ones called tannins. Some trees will hold the brown leaves all winter up until the buds start to swell preceding leaf emergence. This condition is called marcescence.
Soil moisture, cold nighttime temperatures and nutrient availability all affect the amount of anthocyanins and carotenoids leaves can produce, but cool to cold nights, soil on the dry side and bright sunny days produce the most brilliant fall color. Some people mistakenly believe that more rain and soil moisture help fall color, but just the opposite is true. Trees under a slight amount of stress produce the most vivid fall colors.
 Orangeola is one of my favorite Japanese maples and has impressive fall color |
Fall color in north Texas doesn't hold a candle to the magnificent show that trees in colder parts of the country display, but there are some tree choices that have pretty dependable color. My favorites are Texas red oak, ginkgo, Texas ash, bigtooth and Caddo maple, flame leaf sumac, Persian ironwood and most all the Japanese maples.
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