Single Leaf Ash

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 exotic, invasive insect visit, csfs.colostate.edu/eab. For alternatives to this tree visit the Front Range Tree Recommendation List.

SCIENTIFIC NAME: Fraxinus anomala

FAMILY: Oleaceae

Hardiness: Zones 5 to 7

Growth habit: Tree has a round habit as a young tree becoming more upright and elliptical in form. Commonly found in the draws and canyons of western Colorado and southern Utah where more water will collect because of run off or storm events.

Foliage: Unlike the typical green ash which has a pinnately compound leaf the single leaf ash has mostly simple leaves on the stem. Leaves are smooth, glossy and slightly toothed on the leaf margin. The bright green leaves will turn a brilliant yellow color in the fall. From a distance this tree is striking because of its yellow fall color.

Fruit: Winged seed is a samara up to three quarters of an inch in length. Hang on the tree in clusters. Seeds mature in mid-summer and can persist on the tree through the winter.There are many varieties of green ash which are seedless: The male side of this dioecious tree.

Bark: As the main trunk matures the bark becomes dark brown to gray and is slightly furrowed.

Twigs: On young branches light tan in color turning gray with maturity. Twigs are slightly 4-angled when young.

Insects and diseases: No observed pests in its native habitat.

Landscape value: Not commonly found in the nursery trade at this time. This tree has great potential for Colorado’s xeric landscapes because it is tolerant of heat, drought and high pH soils. The current national champion is growing in a red sandstone amphitheater south of Gateway, Colorado.

Information sources:Trees of Utah and the Intermountain West, Utah State University Press, 1998. Michael KuhnsFire Effects Information System. USDA Forest Service.

Photo by Conservation Garden Peak