The red ash tree (Fraxinus pennsylvanica), also known as green ash, is a common North American species. This deciduous tree is found across central and eastern North America, from floodplains to urban areas.
Identifying Red Ash Trees
The red ash typically grows to a height of 50 to 70 feet, occasionally reaching up to 100 feet, forming a single, straight trunk and an oval to rounded crown. Its bark on mature trees is thick and gray-brown, characterized by interlacing ridges that create distinctive diamond shapes.
The leaves of the red ash are oppositely arranged and pinnately compound, typically measuring 6 to 14 inches long. Each leaf usually consists of 5 to 9 elliptic or lance-shaped leaflets, each about 2 to 5 inches long with smooth to slightly serrated margins. The upper surface of the leaflets is medium to dark green, while the underside is lighter green and often covered with short, woolly hairs. In the fall, the foliage transforms into a golden-yellow hue.
Red ash trees produce small, inconspicuous flowers in mid-spring, before the leaves fully develop. These flowers are wind-pollinated, and individual trees are either male or female, meaning both sexes must be present for seed production. The fruit, known as samaras, are single-winged, dry, and flattened, measuring 1 to 3 inches long. These samaras mature in late summer and fall, changing from green to tan, and often hang in drooping clusters, dispersing by wind or water. Younger twigs, new shoots, and winter buds are reddish-brown and have a velvety texture. The tree’s branching pattern is typically opposite.
Growing Conditions and Care
Red ash trees are adaptable, tolerating various soil types from moist, well-drained loams to heavy clays and drier sands. They are often found along riverbanks, in floodplains, and bottomlands, indicating a tolerance for occasional flooding.
For optimal growth, red ash requires a location that receives full sun to light shade, promoting vigorous development and a dense canopy. It can withstand strong winds and atmospheric pollution, making it a suitable choice for urban environments. When planting, select a site that provides ample space to accommodate its mature size, typically reaching 35 to 50 feet wide, to prevent future conflicts with buildings or other trees.
Proper planting involves digging a hole two to three times wider than the root ball, ensuring the top of the root ball is level with the surrounding soil. After placing the tree and backfilling, thorough watering is crucial to settle the soil and eliminate air pockets. Consistent moisture is particularly important for newly planted trees to establish a strong root system, though mature red ash trees are drought-tolerant once established. Pruning should be minimal, performed in late winter or early spring while the tree is dormant, to remove dead, damaged, or crossing branches.
Common Issues and Threats
The emerald ash borer (EAB), an invasive wood-boring beetle from Asia, is the most significant threat facing red ash trees today. This pest has caused the decline and death of tens of millions of ash trees across North America. The EAB larvae burrow into the tree’s inner bark and phloem, creating S-shaped feeding galleries that disrupt the flow of water and nutrients, effectively girdling and starving the tree.
Signs of an EAB infestation include:
D-shaped exit holes (approximately 1/8 inch in diameter) from emerging adult beetles.
Canopy dieback, often starting from the top.
Epicormic shoots (new sprouts) from the trunk or branches.
Increased woodpecker activity, indicated by bark flecking.
Prevention strategies for EAB include quarantines to limit the movement of infested wood and diligent monitoring of ash trees for early signs. If EAB is present, insecticide treatments can protect high-value trees. Systemic insecticides like emamectin benzoate (often a trunk injection, effective for 2-3 years) or imidacloprid (soil drench or injection) are commonly used. Treatments must be repeated every 1-3 years for the tree’s lifetime.
While EAB is the primary concern, red ash trees can also be affected by other issues. Ash yellows, a chronic systemic disease caused by phytoplasmas, can lead to slow growth, smaller and lighter green leaves, and progressive dieback, sometimes resulting in witches’ brooms. This disease, spread by phloem-feeding insects, has no known cure, and severely affected trees may need to be removed. Leaf spot diseases can also occur, though they are generally less severe than EAB or ash yellows.
Ecological Role and Uses
Red ash trees are valuable in riparian ecosystems, stabilizing soil and supporting wetland health. They provide food and habitat for various wildlife:
Seeds are consumed by birds and squirrels.
Foliage and twigs are palatable to hoofed mammals like white-tailed deer.
Red ash provides cover and nesting sites for birds and bats.
It also acts as a host plant for various butterfly and moth larvae.
Red ash wood, though generally considered inferior to white ash, is strong, flexible, and shock-resistant. It is used for tool handles, flooring, and furniture. The wood is easy to work with and takes finishes well, making it suitable for items requiring durability. However, the widespread impact of the Emerald Ash Borer has significantly affected the conservation status and availability of red ash, leading to concerns about its long-term survival in North American landscapes.