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Autumn Purple Ash

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All Ash tree species (Fraxinus) are no longer recommended to be planted in Colorado due to identification of the Emerald Ash Borer (EAB) within state borders. To learn more about this insect visit our EAB Informational Page. For alternatives to this tree visit the Front Range Tree Recommendation List and the Feature Tree Archive.

SCIENTIFIC NAME: Fraxinus americana
FAMILY: Oleaceae

Hardiness Zones 3 to 9.

Growth rate and mature size A fine selection of pyramidal to upright round form. It will grow to a height of 60 ft and a width of 45 ft.

Foliage Leaves are opposite and pinnatley compound, 8 to 15” long, with 5 to 9 leaflets, stalked, 2 to 6” and 1 to 3” wide. Body is ovate-lanceolatle, with acute to acuminate at apex. Usually the margin is remotely serrated. Summer color is dark green and glabrous on the surface with a pale green under the leaf surface. The fall color is a reddish purple that normally lasts 2 to 4 weeks.

Flowers This tree is dioecious or possibly polygamo-dioecious. Both sexes appear in a panicle before the leaves emerge. The corolla absent, with the color being green to purple and blooming in April.

Fruit A 1 to 2” long samara with it’s width about 1/4”. No ornamental color or quality to the fruit.

Bark Gray-brown bark is very smooth in youth, but becoming very deeply furrowed and ridged in just a few short years, with the ridges interlacing to form a diamondback pattern of 2″ thick bark at maturity.

Insects and diseases This tree can have many problems if poorly cared for. It is susceptible to: Cankers, Lilac/ash borer, carpenter worms, and ash flower gall. Recently, the ash sawfly has become a big problem on Autumn purple ash up and down the Front Range of Colorado, chewing leaves in May and June. Ash borer is a big problem in Colorado where ash trees grow.

Landscape value Autumn purple ash is best suited for medium-sized spaces or large spaces, like a park. A small space is not recommended as this can stress the tree and cause a poor-developing root system. Also, it would not be a good tree to set under power lines, as it will grow to a height of 60ft.

Information sources
Michael Dirr, Manual of Woody Landscape Plants (University of Georgia, 1990)
Ohio State University’s Plant Dictionary