A question often asked in the fall is why leaves change from green to beautiful yellows, reds and oranges. Many factors influence this change, including longer night periods and cooler weather. When a tree is exposed to these environmental conditions, it produces less and less green chlorophyll. Other color pigments are already present in the leaf but are masked by the dominant green color of the chlorophyll during the growing season. These colors become more visible as the chlorophyll breaks down. Pigments include various anthocyanins that produce shades of yellow, orange and brown and carotenoids that bring varying shades of red.
Many conditions influence the intensity of fall color. According to a U.S. Forest Service fact sheet, mild days with brisk nights just above freezing produce the best fall color. Conversely, unusually warm fall weather and drought can reduce its intensity.
Because fall colors are so beautiful, many homeowners want trees that turn hues of orange and red in their yards. Autumn is actually a good time to purchase trees due to more optimal planting conditions than in summer, and they are often discounted by retailers this time of year. Be cautious about which trees you purchase, though. Often, the most common trees are not the most adapted to our soils, especially red and sugar maples (Acer rubrum and Acer sacharum respectively). There are many named cultivars of these trees, such as Armstrong, Red Sunset and October Glory. Research possible trees for your yard before shopping, and look for the Latin name listed on the tag to be sure of the exact type of tree it is.
Other colorful fall trees that are less known but are readily available are much better choices than the two listed above. Along the Wasatch Front and other areas with a similar climate, one of the best trees is the Japanese zelkova. It reaches up to 40 feet high and wide in our climate and has burnt-red fall color. Another tree that reaches a similar height is Pacific sunset maple. It has bright orange-to-red fall color.
There are many other smaller trees that also have excellent fall color. One of the best includes Washington hawthorn. It grows to 25 feet high and wide and turns brilliant orange to red. It is drought hardy, adapted to the soil and produces small ornamental fruit that sticks to the tree until mid winter. The fruit decomposes into the soil before warmer weather sets in the next year. Washington Hawthorn is cold hardy in almost all populated areas of Utah.
Other colorful fall trees worth planting that may be slightly more challenging to find include Tatarian maple, Sargent cherry, autumn brilliance serviceberry and American smoke tree. For more information about selecting trees appropriate for the landscape, visit the USU Tree Browser at www.treebrowser.org.