Autumn color is a favorite part of the season. The changing and falling of leaves is also very important to tree survival. The same processes that lead to fall color also enable the dying leaves to return valuable nutrients to the tree.
As leaves fall and decompose over time, nature’s ‘recycling’ begins. In fact, more than half the nitrogen, phosphorus and potassium that leaves contain return to the tree. Appreciable amounts of magnesium and carbohydrates (sugars) are similarly reclaimed. Only calcium is lost in large quantity when the leaves drop. These processes keep trees alive and growing. The spectacular autumn foliage display is actually just a byproduct.
Dull Autumn Color
Some years the colors of fall are simply awe-inspiring. At other times, just ho-hum. So what gives? What makes autumn color so variable? It all starts with a good spring growing season. When this is followed by sunny days and mild drought, leaf colors turn brilliantly red and yellow. However, the precise combination of environmental factors required for spectacular foliage does not always occur. Depending on the growing and weather conditions, autumn trees can range from dramatic to dreary and anywhere in between. It will also vary from one geographic location to another.
Many factors impact autumn’s foliage. Extreme drought and early frosts can injure or kill foliage before the peak of color. Excessive autumn rainfall will slow chlorophyll loss and prolongs leaf retention. In this case, the leaves often succumbs to frost before color even has a chance to develop. Further, cloudy periods also alter the season’s hues, reducing the amount of sugars produced. Prevailing warm night temperatures (above 45°F) increase sugar movement out of the leaves.
With all the possible variable outcomes, it is a truly a wonder that nature puts on such an amazing show for us!
There is obviously an annual cycle of color change. However, the early appearance of fall color is frequently an indication that a tree is undergoing stress. Root damage from construction activity, excessive or deficient moisture, insect or disease attack, salt accumulation in the root zone, girdling roots and other factors are common tree stressors.
Watch these trees closely for signs of insects and disease. Providing optimal growing conditions can also help aid in recover for stressed trees. Proper irrigation and a layer of organic mulch are a great start. Build on this foundation by maintaining soil fertility with slow release fertilizers and ensuring adequate organic matter is present.