Wood County citizens are asking, when will the leaves on our deciduous trees change color and drop from the trees? I try to answer this question with a solid scientific response “When they are ready” …

I thought this is not the best answer, because there is science behind why trees change color and drop their leaves. Each year as the days grow shorter and the weather cools trees in Northwest Ohio transform from lush green leaves into fiery reds, brilliant orange, and vibrant yellows, offering viewers a natural masterpiece. Intriguingly enough, the “fall” colors are always present in the leaves, but they remain masked or overshadowed by an overwhelming number of chlorophyll molecules.

Fall weather exerts its influence as to when the trees will color and drop their leaves. Sunlight intensity, as well as, lowering temperatures, and available water to the plant from the soil will all impact the persistence of leaf drop. Frost and freeze events will hasten the occurrence. Trees will start dropping their leaves to conserve water that would be lost during the winter. Finally, it is thought with our continued warm temperatures and dry droughty conditions that fall coloration of our deciduous trees will be later than usual and colors not as intense.

Conifers on the other hand are already exhibiting their normal seasonal needle drop. A definition of a conifer is a tree that bears cones and needle-like or scale-like leaves that are typically evergreen.

Despite being called evergreens, conifer species like pine, spruce, and arborvitae shed their needles in the fall. Often, this needle drop goes unnoticed. During times of drought conditions, conifers often become stressed. When this occurs inner needle yellowing followed by needle drop is more noticeable. How dramatic the needle drop appears also depends on the amount of growth that occurred in previous years. Robust growth results in a lot of needles turning yellow, conversely, limited growth years means fewer needles turning yellow and dropping. It can be quite alarming to a tree owner when large numbers of needles turn yellow all at the same time. This year the color change and the number of needles turning color has been particularly noticeable.

Needle retention varies within the conifer species. Pines (Pinus spp.), including the Austrian, Red, and Scotch, retain their inner needles for three years, while the White pines shed their inner needles every two to three years. Spruces (Picea spp.) retain their inner needles for five or more years. The Arborvitaes (Thuja spp.) retain their inner scale like needles between every one to three years depending on the species. All these conifers shed their older needles located along the interior of the branches first by turning yellow, then brown, finally dropping. At the end of seasonal needle drop the conifers retain only the more recent growth on the trees.

Like most events in nature, there are caveats to every rule. Interestingly, conifers such as Bald Cypress (Taxodium distichum), and Dawn Redwood (Metasequoia glyptostroboides) are deciduous evergreens which lose all their needles each fall. Unfortunately for these deciduous conifers, it has led to the demise of some of these trees when a new owner does not know that the loss of these needles was a normal annual event.

In conclusion, no one has ever topped the metaphorical explanation written by Aldo Leopold in his Sand County Almanac:

“Pines have earned the reputation of being ‘evergreen’ by the same device that governments use to achieve the appearance of perpetuity: overlapping terms of office. By taking on new needles on the new growth of each year, and discarding old needles at longer intervals, they have led the casual onlooker to believe that needles remain forever green.”

“Each species of pine, spruce, and fir has its own constitution, which prescribes a term of office for needles appropriate for its way of life. Thus, the White pine retains its needles for a year and a half; the Red and the Jack pines retain needles for two and a half years. Incoming needles take office each June and outgoing needles write their farewell addresses in October. All write the same thing, in the same tawny yellow ink, which by November turns brown; then the needles fall and are filed in the duff to enrich the wisdom of the stand. It is this accumulated wisdom that hushes the footsteps of whoever walks under the pines.”