Here it is the last full week in October and the fall colors are just beginning to show their color. The changing hues of fall leaves depend upon many factors, including geographical location, growth habit, plant pigmentation and weather.
The hot colors of fall are the opposite of spring’s cool tones. The ruby red, burnt orange, burnished gold and canary yellow typical of the fall season derive more from the foliage of deciduous plants than from flowers. Because of the brilliant colors and sheer volume of leaves, fall foliage defines the season.
Fall does have its own flowers, such as mums and dianthus, but the fiery foliage of maples, oak and birch comes to mind first when we think of a fall scene. These flaming foliage colors seem hot and vibrant, intense and exciting after the overwhelming greenness of late summer. Set these colors off against the summer sky of purest blue, no painter could devise a more exciting color scheme.
The intensity of any year’s changing fall foliage depends on many factors, most of them under Mother Nature’s control. Red and scarlet autumn displays do not occur every year, because weather strongly influences the intensity of red pigment. Yellow pigments are usually more predictable and less influenced by weather.
The best red displays happen during years of abundant moisture, when fall days are warm and sunny and nights are cold. Moisture from summer and early fall rain prevents the aging leaves from drying out and dropping prematurely before they change color.
In years of drought, as we are seeing this year, or even in years when late summer and fall rains are sparse, irrigating the trees and shrubs not only helps prepare them for winter dormancy, but also encourages a better fall color display.
Some trees and shrubs, such as the soapberry tree and sumac, color up early, turning scarlet yellow and red, respectively by late September. Others such as birch and oak remain green throughout October and sometimes into early November.
While the homeowner cannot control weather variations from year to year, they can maximize their fall colors. They should start by choosing trees and shrubs known for their fall colors, then enhance their display by planting them in sites that receive at least six hours of full sun per day in autumn.
Remember that changing angle of the sun means that shadow lengthen, as the days get shorter. Buildings and tree shadows may shift enough at this time of year to cast unwelcome shade on some garden beds that were once sun-filled in the summer.
West and south facing location are usually best for fall colors. Gardeners will find the brightest red-orange colors of a Caddo maple appears on the west side of the house. A burning bush, changes to blood red when in full sun, but becomes a deep rosy pink when grown in the shade. A gardener should design the fall landscape so that they are looking at the west-facing sides of those shrubs and trees chosen for fall foliage.
This is not based on research, but some horticulturists have found that when they are not sure what color a tree or shrub will turn in the fall, they base their educated guest on the color of the plants summer leaves. Those trees and shrubs that summer foliage is on the yellow side of green tend to turn yellow or gold in the fall. Those plants with darker green or bluish green foliage are most likely to become red or purple. Try it and see if this is not true.
One other note about choosing trees and shrub for fall color. Choose those trees and shrubs that are adapted to Oklahoma. Remember native plants are always the best choice.