All summer they’ve remained hidden beneath a green cloak. But as fall continues, the parade of brilliant tree leaf colors will slowly put on a spectacular show across Kentucky.

The fall colors have been in the leaves all along, but they were masked by chlorophyll, a green pigment that combines with sunlight to produce food for tree growth. It might surprise you to know that this rebirth of color is caused by fewer hours of daylight, not “Jack Frost.”  According to Billy Thomas, University of Kentucky extension forester, this “chemical clock” is activated by shorter days alerting trees to shut down chlorophyll production in preparation for winter. So trees use chlorophyll faster than it’s produced. This removes the green mask and the brilliant fall color show begins.

The all colors typically peak in mid-to-late October. Because Kentucky has such a diverse climate and soil composition, many tree species common to both northern and southern states grow here. This provides a variety of fall colors for us to enjoy as we walk or drive through state and local parks and national forests. Our nature sanctuaries and arboretums also have many tree species that erupt with color in the fall. 

Maple, dogwood, black gum, oak and sassafras trees produce various shades of red color. Trees that provide a range of orange and yellow colors include yellow-poplar, birch, hickory, beech and white oak. Since black gum and sumac trees shut down chlorophyll production early, they are the first to reveal fall colors. Both change from green to red leaf by leaf. No one leaf seems to be all green or all red at the same time, giving a spotty appearance throughout the trees.

These two trees have characteristics that make them easy to identify. Black gum is one of the few trees to have right-angled branching. This means the limbs come away from the main stem at a straight 90-degree angle. Other tree species have limbs with some angling. Sumac is also easy to identify because the leaflets growing along the stem resemble teeth on a saw blade from a distance.

Trees do more than just give us a spectacular color show. They also make an important contribution to our continuous ecological system. As leaves drop to the ground, announcing winter’s approach, minerals previously taken into trees are recycled. The leaves decompose and return nutrients to growing plants and trees while adding organic materials to the soil.

While the colorful leaves of fall gently float to the ground, next spring’s leaves are wrapped tightly in buds, waiting to unfurl and replenish the air by absorbing carbon dioxide and giving off oxygen.

Rob Amburgey is a Jessamine County Extension Agent For Agriculture and Natural Resources.