Now and within the next several weeks, many Pennsylvania plants will go through their traditional color change. I have watched the change occur as I drive from my home to Pine Gove Mills, going up through the mountain on state Route 26. I do believe that the severe windstorms we experienced this year and the dry weather has affected the trees and the duration and intensity of the colors. I know that many of my trees have already shed their leaves.
Usually, some of the brightest reds are seen on Black Gum and Red Maple. My Black Gum and Red Maple trees have already shed their leaves. They are both common trees and can be seen along the roads and in woodlots. Both do well in wetter soils. In fact, another common name for Red Maple is Swamp Maple because of its ability to survive in wet spots.
Black Gum tends to stand out in a group of trees because of its slightly horizontal branch pattern. Red Maple can be easily identified by it bright gray bark.
As the season progresses, new red and orange colors will appear from Sugar Maples and various oaks. Sugar Maples will often display a mottled color pattern of red, orange and yellow colors on the same tree. This color variation adds to its value in the landscape setting.
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Red, Black, Pin and Scarlet Oaks all develop a red color. Red and Black Oaks may develop a dull red color, but Pin and Scarlet Oaks will develop a brilliant scarlet color every season unless a severe early frost kills the leaves. All of these oaks have deep lobed leaves with small bristles at the end of each lobe.
Additional red color can be seen on Flowering Dogwoods, Staghorn Sumacs, Sassafras and several species of Hawthorn. Native wild cherry species will form a red-to-red orange color in most seasons.
Poplars will turn yellow to yellow green. The Birch follows poplars, the first to turn yellow. Poplar is a fairly open tree with light colored bark, while most Birch have dark brown to black bark. Paper Birch, native to northern counties, has a snow-white bark and gives one of the brighter yellows.
Most of the Hickories and Tulip trees will stand out in a woodlot or forest area with their very clear yellow leaves in the fall. They add a great deal of color because all their foliage turns at the same time. Other plants often turn color gradually, so the summer blends with the fall shades. The sad thing is that we lost some beautiful large hickories in the last windstorm.
Norway Maples have escaped into the countryside where they grow among our native trees. They appear as a dense broad-spreading tree with a rounded crown. The have a deep green summer color and a bright yellow fall color.
In addition to the red, orange and yellow leaves, you might come across a few purple tones. These will probably be one of the several Ash species found across the state. Ash appears as a coarse-headed tree with several strong limbs and smaller twigs toward the tips of the branches. The problem with Ash is that the Emerald Ash Borer has eliminated most of the Ash trees. We lost many Ash trees on our property.
Plants also add to the fall color display. Red and orange tones can be found in many of the native Viburnums, such as Arrowwood, Nanneyberry and Blackhaw. Japanese Barberry will appear as a bright red spot in a woodlot or pasture and Bridalwreath Spirea and Blueberry will also turn red as the weather turns colder.
Fall leaf colors come about through changes in temperature and moisture. As fall approaches, the leaf no longer produces the green chlorophyll. Most leaves contain a yellow color that is masked by the green color. With a decline in green color, yellow undertones become visible. If there’s no yellow pigment in the leaf, the leaf will go from green to brown before dropping.
The development of red, orange and purple colors in other plants is not as simple. To secure these colors, the leaves must produce another pigment called anthocyanin. Production of anthocyanin is greatest when we have sunny days and cooler nights. The plants’ internal chemistry reacts with anthocyanin to determine the final leaf color.
Contrary to popular belief, a frost will not cause a change of leaf color. A light frost will often speed the breakdown of the chlorophyll and bring the yellows to the surface, but a heavy frost can destroy the leaf and produce a brown color even in leaves that should turn bright colors.
Bill Lamont is professor emeritus of vegetable crops in the department of plant science at Penn State and can be reached by e-mail at firstname.lastname@example.org.