by Ann Farnham, LLA

At this time of the year we are especially fortunate to live in a region which displays brilliant leaf color in many of the abundant deciduous trees. The colors vary from yellow to orange, and bright red to purple. This does not happen throughout the world, but only in the Northern hemisphere and one small area in South America. The Northern hemisphere regions include Eastern Asia, Japan, Southwest Europe, and the United States and Canada. In the United States and Canada the foliage display ranges from Southeast Canada and the Northeastern United States, and its high altitude areas, like the Great Smoky Mountains and the Blue Ridge Mountains to the Rocky Mountains of the Western U.S. and Canada.

The brilliance of the color changes from year to year depending on weather conditions: a warm, wet spring, a summer which is not too hot and dry, and a fall with plenty of warm, very sunny days, lessened moisture, and cool nights.

By Berean Hunter (Own work) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)%5D, via Wikimedia Commons

The process, which some of us learned in our high school biology classes, begins with the fact that deciduous, green leaves contain chlorophyll, which in the presence of sunlight, water, warm temperatures and carbon dioxide, produces sugars which feed the plant, tree or shrub. Leaves also contain carotenes and xanthophyll, pigment compounds whose yellow colors (the colors seen in egg yolks, carrots and flowers) are masked by the green chlorophyll. When the days become shorter, the chlorophyll has insufficient light to continue making sugars and breaks down, making the green color disappear; the other pigment compounds then become apparent. Meanwhile, the plant begins to form a membrane between the leaf and the leaf stalk, cutting off the movement of the leaf’s sugars to the rest of the plant, sealing off the leaf and gradually severing it. The sugars become entrapped in the leaf. Another pigment compound, anthocyanin, then appears as a result of the accumulation of the sugars; its appearance also depends on warm and bright sunny days followed by cool nights, under 45° but above freezing. The anthocyanin contains the red to purple pigments which we see on Sassafras, Red Maples, Fothergilla, and Flowering Dogwood, among others.

If a plant is located in a shady area it will not produce very brilliant colors as the process requires a certain amount of bright sunshine. A plant might exhibit much brighter color on its sunnier side, as well. A cloudy, rainy and warm fall restricts sugar production by the carotenes and xanthophyll, and what is produced continues to be transported to the trunk and roots, not “entrapped” in the leaf. Thus, poor or no color.

Some plants’ leaves will always turn yellow regardless of weather conditions, and some, such as Beech and some oaks, simply turn brown. All deciduous leaves eventually fall, some turning brown only after they fall from the plant, tree or shrub.

Needled evergreens such as pines, spruces and firs have needles which are covered with a heavy wax coating and have chemical fluids inside the needles which resist freezing. However, needled evergreens do experience periodic leaf fall and some, such as certain arborvitaes and junipers, change color.

Near freezing temperatures, low nutrients and other environmental stresses can also cause more and premature red in leaves.

This is an opportunity to encourage all gardeners to compost and use their leaves. A mulching mower chops up the leaves and returns them to nourish the lawn (mow frequently, however), and a blower-vac can chop up leaves into a bag for later composting and use. These chopped leaves make a fine mulch on beds. Pine needles also make an excellent mulch, being acidic in nature, especially beneficial for rhododendron, azalea, and other broad-leafed evergreen plants. 

• To calculate the economic and ecological benefits of the trees on your property. go to treebenefits.com.

• To estimate the age of a tree, go to mdc.mo.gov

The purpose of the Ewing Township Plant of the Month is to call attention to Ewing Township plants of note based on their beauty, size, historical significance or threat, and thus engender a greater appreciation by residents for the plants in our community.

The Ewing Environmental Commission welcomes suggestions for the Plant of the Month from all Ewing residents. Let us know about your favorite trees, shrubs, flowers, and concerns in Ewing Township and perhaps one will be selected for the Ewing Township Plant of the Month.