Green Ash

Fraxinus pennsylvanica

Green ash can grow fast reaching to about 60’ x 40’ in an oval shape with adequate watering, but typically it is a medium growing tree. A hardy selection and a once top-choice for city street trees because of its high pH and salt tolerance in soils. However, since the discovery of the invasive, destructive beetle, Emerald ash borer, it has since lost its desirability. It has brown to yellow fall leaves. The females produce an incredible amount of fruit which can be a nuisance.

Common Problems

Environmental

Girdling roots are common and should be watched for and pruned, if necessary, at planting. Sunscald is very common on the southwest trunk of young trees (< 3 years) and recent transplants and should be wrapped from November through March to avoid the damage. Must be pruned as it grows to establish good branch structure otherwise it will likely develop poorly and fall apart in wind and snow storms.

Diseases

Ash are affected by a number of leaf fungi that are usually not bad enough to warrant chemical control. Just rake up and dispose of infected leaf tissue when it falls to the ground. Some cankers can be found on trunks and branches, but usually only on stressed trees. Verticillium Wilt attacks stressed trees and will cause severe branch dieback or whole tree death in some cases. Ash ring spot is a virus that causes some twig dieback, but it is rare and often minor.

Pests

Emerald ash borer, an invasive beetle, successfully kills >99% of ash trees as it moves through an area. Comparable to Dutch Elm Disease, it is likely that many North American ash species will seccumb to this destructive beetle unless treated with insecticides.

Ash trees are also susceptible to a number of native pests like Lilac/Ash Borer and Aphids. Lilac/Ash borer will damage the trunk and kill the tree if left untreated for many years. Aphid populations can be heavy, but do little to stress the tree health. They are, however, unsightly and the honeydew can be a nuisance on walks and cars. Ash Flower Gall attacks the developing flowers in early spring leaving an unsightly brown crusty ball and often stunting leaf and twig growth for the year.

Cultivars

‘Marshall seedless’, ‘Summit’, ‘Patmore’, ‘Cimmaron’, ‘Newport’ are the most common. Summit is very popular, but caution is needed as it tends to grow multiple trunks and branches making it very weak and highly susceptible to failure in winds as it matures. It is very difficult to prune into a strong structure.

History and Use

Very common street tree. Wood can be used in furniture and flooring.