SCIENCE OF FOLIAGE
The fall color show in Oklahoma is different every year based on temperatures, light intensity, moisture in the ground and weather patterns
We have been blessed with absolutely gorgeous fall weather the last few weeks as many spring flowers are blooming again and the hardy mums have been bursting out in their dazzling colors.
The leaves on our deciduous trees are changing color, and many leaves already are dropping. You can almost see the changes by the day as the leaves go through their final stages of life and we wrap up another growing season.
There is amazing science to the annual fall color ballet before the leaves separate from the tree and drop or float to the ground. The show is different every year based on temperatures, light intensity, moisture in the ground and weather patterns.
Day length is the trigger that incites fall color as the days get shorter. Deciduous trees and shrubs read these shorter days as the alarm clock to switch from growing full speed and manufacturing carbohydrates, sugar and others foods for the growing plant to winding down the season and storing food for the winter hibernation.
Day length triggers the fall color, but moisture plays a major role in intensity. Fall color is generally much less intense in a dry or drought year and better in years with regular rains where the trees have adequate moisture in their root zone and good sugar production. Early or sudden cold fronts can shorten or rob us of the best of the fall tree colors. A hard early freeze can interrupt the seasonal color and move us directly to brown leaves or leaf drop on many trees.
The color is best in years when we have adequate soil moisture and gradually declining day and night temperatures so that we get the full program of fall color instead of an abbreviated show. Some deciduous trees and shrubs start this process earlier than others so that some trees will have colored and dropped leaves before other species even start to color up.
As the days shorten and the temperatures cool, trees will start to bring sugars and carbohydrates out of the leaves and down into the branches, trunk and roots to store food and energy for the long, cold winter to come.
Three pigments drive the fall color dance.
Chlorophyll is the green pigment we have seen all spring and summer in most leaves and it converts sunlight and moisture into sugars that power our plants.
Carotenoids are the orange, yellow and brown tones we see in carrots, corn, bananas and daffodils and are present in the leaves all season but are usually masked by the green chlorophyll.
Anthocyanins produce the red and blues we see in strawberries, blueberries, apples, grapes, cherries and plums. Anthocyanins are only produced in most leaf cells in cooler weather when excess sugar is trapped in the leaves in the presence of bright sunlight.
Chlorophyll production slows and finally stops as the temperatures get cooler and the days get shorter. As the chlorophyll disappears from the leaves we get to see the colors of the carotenoids and anthocyanins that are still in the leaves. These result in the fall colors we anticipate each fall as the trees transition from summer growing to winter.
Different species produce different fall colors depending on their chemistry and the weather. Take time to enjoy the bright yellow of the poplar trees to the red and brown of oaks, the red, yellow and orange of maples. The leaves will then fall to the ground, where they will provide mulch to the landscape below or can be composted to add to your soil to make a better growing environment for future gardens or trees.
We hope the temperatures cool gradually and we get the full fall color season before a hard freeze in your neighborhood.
Don't forget to be planting pansies, ornamental kale and cabbage for winter color, and sow tall fescue seed for green turf this winter. Shop for daffodils, tulips, hyacinth and crocus bulbs to plant over the next few weeks to get a beautiful show of flowers to kick off spring next year in your yard.