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Fall Leaf Colors Depend On Species, Conditions
By Norman Winter
Central Mississippi Research & Extension Center
Despite droughty, warm conditions this October, fall leaf colors have been very good. This brings up the question of what makes fall color good.
Start with a good species. The trees that have been most spectacular in my neighborhood are the hickories. Hickories, have bold, yellow leaves that hold for a long time.
Sweetgums are next on my dependable list for fall colors. With its attractive palmate leaves, the sweetgum provides some of the deepest shades of orange and crimson. I became the joke of the neighborhood when I bought one and planted it in my landscape. But jokes aside, it is hard to beat.
Some horticulturists believe the ornamental pear is over planted, and I started to buy into that idea. But this tree is one of the most dependable for color from year to year.
When we look at fall color scientifically, words like carotenoids, pigments and chlorophyll enter into the discussion, as does auxin, gibberellins, other growth hormones and enzymes.
Good conditions boil down to cool night temperatures and warm, sunny days make great fall colors. Climatic conditions have the most effect on the production of anthocyanin pigments which intensify the red and scarlet colors. Conditions that most favor these colors are sunny days and nighttime temperatures between 45 degrees and freezing.
Even though the chlorophyll content of the leaf declines in the fall, it is still important that photosynthesis take place. If an abundance of cloudy weather prevents photosynthesis from occurring, leaf color will be mediocre even if temperatures are ideal. This also can weaken the leaf, making it easy for a northern wind to blow it off the tree.
Cool night temperatures limit the movement of sugar from the leaves. It also reduces the rate of respiration in the leaf, so some sugars are converted to carbon dioxide. Those retained are converted to colorful anthocyanin pigments. Even with perfect climatic conditions, if we don't have the best species of trees, we are lost from the start.
Other than hickories, the best trees for yellow are the green ash, gingko and elm. The best trees for red, in addition to sweetgum and ornamental pear, are the red oak, black gum, red maple and Japanese maple. Two others which we overlook are the dogwood and the new Indian varieties of crape myrtles.
One of the prettiest trees starting to catch on across the state is the Chinese pistache. This tree is used sometimes as a rootstock for the pistachio in California. It thrives in Mississippi and gives us some of our prettiest oranges and reds. It is a medium to small tree and will fit nicely in urban landscapes.
The Chinese pistache forms a spreading, umbrella-like canopy and attains a mature height of 40 to 50 feet with a width of 30 feet. This long-lived species should find wide acceptance for the landscape.
With good management, Chinese pistache grows 2 to 3 feet per year. Eliminate competition from grass or turf by mulching, proper fertilization and adequate watering during the summer months. With such a growth rate, the Chinese pistache will reach a reasonable size and begin to play a major role in the landscape within just eight to 10 years.
These trees can be seen in and around the Hinds Community College campus in Raymond as well as at strip malls in Jackson, in Grenada and along the Coast. While the ornamental pears sometimes break in the face of winds and ice, the Chinese pistache has an extremely hard, durable wood. Female trees produce colorful fruit suitable for use like holly berries in decorations.
Fall is a great time to purchase and plant trees and shrubs. Nurseries have good selections and a staff to help with your plans. Root growth continues in the fall even though top growth may have ceased, so planting now gives plants almost a full growing season's advantage over planting next spring.