Water Ash Fraxinus pennsylvanica

Green ash is a native, medium-sized, broadleaf, deciduous tree in the olive family (Oleaceae). Green ash is native to central and eastern Canada and the west central and eastern United States. Habitats include floodplains, mesic woodlands, riverbanks, swamps, and open fields. In North Carolina, this tree is often found in bottomlands and swamps, especially along brown water rivers and the low ground of Piedmont and lower mountains. The meaning of the specific epithet is “Pennsylvanian.”

Green ash prefers full sun to light shade, moist, well-drained soils of clay or loam and will tolerate occasional flooding. It is probably the most adaptable of all the ashes and is deer resistant. It is tolerant of drought, wind, moderate salt, and alkaline soil. It transplants well and grows well in a variety of locations and soils. 

Green ash may grow 50 to 70 feet tall and 35 to 50 feet wide with a trunk 2 to 3.5 feet across. Young trees are pyramidal, but as the tree matures it becomes more rounded with an irregular crown. The bark is thick, gray-brown with shallow furrows and crisscrossing ridges which form diamond patterns. The leaves have 7 to 9 leaflets. Small, light green to purple flowers, with no petals, mature in loose panicles in early spring. The female tree produces a single-winged, dry, flattened samara with a slender, thin seed cavity that matures in the fall. These can be numerous and can make a mess when they fall to the ground, but the seeds provide food for many kinds of wildlife. Male trees are usually preferred in the home landscape because they do not produce fruit. 

Across its wide distribution, this species is highly variable, and many of these variants have been given formal taxonomic status. Variation in leaf and twig hairiness, leaflet width and other morphological characteristics are included in a broadly defined green ash species. 

Green ash made an excellent specimen or shade tree. It was appropriate for native, children’s and butterfly gardens. Planting new green ash trees is no longer recommended. The tree is very susceptible to infestation with the emerald ash borer. This borer will typically kill an ash tree within 3 to 5 years after infestation. It is very difficult to eradicate this pest which feeds under the bark and bores into wood. The emerald ash borer is native to Asia and was first discovered in the U.S. in 2002. It has now spread to several additional states in the northeast and upper Midwest and is expected to continue spreading. This borer now constitutes a serious threat to all species of ash in North America.

Quick ID Hints:

• grayish-brown bark with diamond-shaped ridges on older trees
• pinnately compound leaves with 5 to 9 leaflets that are ovate to lance-elliptic
• leaflet undersides are green and margins are crenate to serrate from the mid-leaf to the tip
• short-winged stalks on the leaflets 
• leaf scar is semi-circular
• flowers appear after the leaves emerge
• female trees produce clusters of winged samaras

Insects, Diseases, and Other Pest Problems:  Green ash trees are generally susceptible to several insect problems including the Emerald ash borer, lilac borer, carpenter worm, oyster shell scale, leaf miners, fall webworms, ash sawflies, ash leaf curl aphids. Potential disease problems include fungal leaf spots, powdery mildew, rust, anthracnose, cankers, and ash yellows. General ash decline is also a concern. Brittle branches are susceptible to damage from high winds and snow/ice. See potential insect and disease problem factsheets to the left.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University