Fall Leaves!

The leaves they are a changing!  The temperatures and day lengths also are a changing.  These happenings are very closely related as the changes in day length, light intensity and temperature (night temperatures in particular) leads to the fall color.  As the earth rotates and we get fewer hours of sunshine each day and our nights get longer, the temperatures slowly drop leading to autumn and then winter as we get less and less sunshine.

Some years the reds, oranges and yellows of our fall tree leaves are more intense and more plentiful than other years.  The actual temperatures, moisture levels and cloud cover can cause this variation from year to year.   The reds are best when we have a number of warm sunny days with crisp cool nights but without any actual freezing temperatures.  Trees produce a lot of sugars in the daytime as they do their photosynthesis but the cool night temperatures keep the sugar sap from flowing back through the leaf veins and into the stems, branches and trunk of the tree.  That is when anthocyanins or red pigments that are mainly produced in the fall come into play.  These anthocyanins allow the tree to recover nutrients from the leaves for the next season before they fall off the tree.  These anthocyanins give leaves their shades of red, purple and crimson. 

The yellow, gold and orange colors are created by carotenoids that are always in the leaves but become unmasked as the green chlorophyll shuts down production during the short cool days of autumn.  The same carotenoids are what give color to corn, carrots and bananas where those vegetables or fruit don’t have chlorophyll at work.  Since carotenoids are always present in leaves those colors are fairly consistent from year to year and the trees that produce yellow leaves each fall do not change as much from year to year in response to weather. 

The weather earlier in the growing season can also impact fall color.  Severe droughts like the last two years can delay the start of fall colors and reduce their intensity.  A warm wet autumn will reduce the brightness of fall colors.  An early hard frost or freeze will just kill the leaves and cause them to drop early.   The best fall colors come after warm, wet springs, a summer that is not too hot or dry and a fall with warm, sunny days and cool nights.  Much of our state has had the best conditions in several years to produce good fall color so if we can avoid an early hard frost we are expecting a great show of fall color.

Make time to drive to southeast Oklahoma and the Talimena Scenic Skyline Drive for the best tree color in our state, to visit the arboretum at Will Rogers Park or just drive through neighborhoods to soak in the show. 

As you enjoy the annual symphony of fall tree color don’t forget this is a great time to plant new trees and shrubs.  You can also plant pansies for show all winter and spring flowering bulbs to announce the arrival of next spring.


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