Cooler nights, apples, pumpkin flavored everything, and football can only signal one thing, fall is here. This year has been a wonderful one to see fall color in Nebraska’s landscape. What exactly causes this fall color and how can we see it every year? The answer is more scientific than we think.
The science behind leaves is as complex as it is interesting. The colors that we see in the leaf comes from cells called pigments. The green pigments that we see are called chlorophyll. Some of the other pigments that offer the other fall colors are present all year long, they are just covered up by the green chlorophyll. When the days become shorter and cooler, the production of chlorophyll slows down and eventually stops. When the green color disappears, the other hidden pigments are now able to show off their full beauty. Carotene and xanthophyll are the yellow pigments that are produced in the foliage all year long, but aren’t present until the chlorophyll disappears. The anthocyanins are responsible for the red and purple pigments. The anthocyanin production increases with the increased levels of sugars in the leaves.
Often Jack Frost gets all the credit for the fall display, but actually he has little to do with it. Fall color is controlled by the plant’s genetics and the environment. The weather conditions such as temperature, moisture, rain, wind and the availability of sunlight impact the quality of the fall color. Clear days, cool nights, and dry conditions provide the best fall color. The two-tone effect that often happens in green ash can be explained by the outer branches being exposed to sunlight, while the inner branches are shaded. Heavy winds, rainfall, freezing temperatures can kill the leaf tissue and shorten the fall color display.
Often we only think of fall color in our deciduous trees, but evergreen needles change color in the fall too. It is a normal occurrence called natural needle drop. The older interior needles of pine and spruce are turning yellow and eventually drop from the tree. The older needles that are lost are usually located closer to the inside of the tree or trunk. Factors that increase the stress on an evergreen can intensify the autumn needle drop. These stress factors can include drought, herbicide injury, root damage, or insect or disease damage.
Like many living things, evergreen needles also have a lifespan. Pine trees hold their needles for 2-3 or more years. Spruce trees hold their needles longer than pines, usually around 5-7 years. After the needles have lived their lifespan, they fall from the tree. Some trees, like the white pine, make it easy to see the needle drop.
Looking for a plant that will provide fall color? If you are looking for an orange color, sugar maple, serviceberry, some crabapples, and oakleaf hydrangea might be worth a try. White, red, and scarlet oaks, flowering pears, Ohio buckeye, red maple, and the burning bush provide red color. Yellow fall foliage plants can include the Kentucky coffeetree, Norway maple, silver maple, cottonwood, elm, and quaking aspen. Purple is a little more difficult to find, but the gray dogwood and some viburnum species can provide the splash of color that you are looking for. Ash is one tree that does offer good fall color, but it isn’t recommended for our area due to the looming infestation of the Emerald Ash borer in our state.
Embrace fall. Select plant material that will offer multiple seasons of interest then kick back with a pumpkin latte and enjoy the natural display of beauty.
Elizabeth Killinger is the Horticulture Extension Educator with Nebraska Extension in Hall County. For more information contact Elizabeth at firstname.lastname@example.org, her blog at https://huskerhort.com/, or HuskerHort on Facebook and Twitter.