Autumn Purple ash is a rapidly growing deciduous shade tree that bears red-purple to maroon colored fall foliage. A male-gendered tree that will not produce seeds, it is a cultivated variety of white ash (Fraxinus americana) that is native to much of the eastern United States. Grow it successfully in U.S. Department of Agriculture hardiness zones 4 through colder winter areas of zone 9.
This white ash tree was discovered at the University of Wisconsin by Karl Junginger of McKay Nursery, Waterloo, Iowa. It was assigned the cultivar name "Junginger" and released into the nursery trade in 1956. Today it is more widely known by its trademark name, Autumn Purple.
A single trunk supports a rounded canopy of foliage that matures to an overall height of 40 to 50 feet tall and 35 to 40 feet wide. The leaves comprise five to nine tapering oval leaflets with a pointy tip, creating a feathery, fine texture across the branches. These deep glossy green leaves blush slightly with some yellow in fall, but they primarily attain red-purple to maroon shades before dropping off. Non-showy clusters of male flowers occur in spring and do not yield seeds.
Tremendously versatile, Autumn Purple ash grows in acidic or alkaline soils that are fertile and moist, ranging from well-draining to occasionally soggy, such as after a heavy rainfall. Best growth results when the tree is in a deep soil. Full sun exposure ensures a well-shaped, rounded canopy and best fall leaf coloration. It grows well in partially shaded spots, too, but with no fewer than five hours of direct sun daily.
The Autumn Purple ash makes an exceptional ornamental shade tree for spacious lawns. Avoid planting it where roadways, sidewalks, or concrete curbing limits the spread of its extensive root system. If a spacious median is provided, it makes a beautiful avenue tree. Its fast growth, resistance to wind, attractive habit and foliage makes it among the finest white ash tree varieties for the landscape, according to the University of Connecticut.
This ash tree does not fare well in prolonged droughts and should be irrigated deeply to prevent twig dieback or premature leaf drop. Monitor Autumn Purple ash for boring insects like ash borer, lilac borer and carpenterworm, which tend to attack young twigs and are most damaging when trees are stressed from drought or other problems. The most serious disease is ash decline, which is caused by many factors including a microplasm organism, according to the U.S. Forest Service. Ash decline occurs on older trees and those that are growing in dry, infertile soil conditions. Because it remains susceptible to ash decline, do not over-plant this tree in landscapes to avoid massive loss of shade trees once this disease appears in the neighborhood.