The Fraxinus genus, commonly known as ash, comprises numerous species that have been historically prominent fixtures across North American forests and urban developments. These deciduous trees gained widespread adoption in landscaping due to their adaptability and rapid growth rate, making them a favored choice for street planting and residential shade. Beyond their aesthetic appeal, ash wood has provided valuable timber for centuries, contributing significantly to various industries. Understanding the modern viability of planting a new ash tree requires a careful analysis of its enduring benefits weighed against a modern, pervasive biological threat.
Why Ash Trees Are Valued
Ash trees are prized in urban settings for their ability to quickly establish a robust and symmetrical canopy, providing substantial shade relatively rapidly compared to other hardwood species. The structure of the tree is typically strong, developing a uniform, oval to round shape that requires minimal corrective pruning during its early stages. This consistent growth habit made it a reliable choice for creating streetscapes with a cohesive, planned appearance.
Aesthetic value is added by the tree’s foliage, which often displays a clear, vibrant yellow, maroon, or deep purple color during the autumn months before leaf drop. The upright branching pattern allows for good light penetration beneath the canopy while still offering cooling shade during summer. This combination of fast growth and appealing form cemented its place as a desirable landscape tree.
The wood of the ash tree is highly regarded for its unique combination of strength, flexibility, and shock resistance without being excessively heavy. This makes it a preferred material for specific applications where durability is paramount, such as tool handles, flooring that must withstand heavy wear, and, famously, the production of wooden baseball bats.
The Dominant Drawback: The Emerald Ash Borer
The most significant contemporary challenge to planting or maintaining ash trees is the presence of the Emerald Ash Borer (EAB), an invasive, small, metallic-green beetle native to Asia. Accidentally introduced to North America, it quickly began devastating native ash populations. The EAB is responsible for the death of tens of millions of ash trees across the United States and Canada since its discovery in 2002.
The borer kills the tree when the adult female lays eggs in the bark crevices. Upon hatching, the larvae bore into the tree and tunnel through the phloem and outer xylem, the tissues responsible for transporting water and nutrients. These serpentine feeding galleries effectively girdle the tree internally, severing the vascular system and preventing the flow of water and sugars.
Infestation symptoms often become visible in the canopy only after two to four years of larval feeding have occurred inside the tree. Early signs include thinning of the canopy and dieback starting at the top of the crown, followed by the appearance of D-shaped exit holes left by the emerging adult beetles. The tree’s reaction to the damage often includes prolific sprouting of suckers, known as epicormic shoots, from the trunk and roots below the feeding zone.
Because the EAB can infest and kill trees of all sizes, its spread has been rapid and devastating. The beetle’s short life cycle allows populations to multiply quickly and overwhelm the host tree’s defenses, leading to near-total mortality in untreated areas. Due to the nearly complete susceptibility of all native North American ash species, planting new ash trees is highly discouraged where the pest is established or anticipated.
The sheer scale of the infestation has dramatically altered forest composition and urban landscapes across the eastern half of the continent. While some native resistance may be observed in certain individual trees, the vast majority succumb to the infestation within a few years of initial attack.
Practical Maintenance and Growth Habits
Even without the threat of the EAB, ash trees present common maintenance challenges. One notable issue is the prolific production of seeds, particularly in female trees. These samaras, often called “helicopters,” drop heavily in the spring and early summer, creating substantial litter on lawns, sidewalks, and gutters that requires regular cleanup.
The root systems of mature ash trees can also become a nuisance in residential settings, as they tend to grow relatively close to the soil surface. These aggressive surface roots can lift and crack sidewalks, driveways, and foundations, requiring costly repairs over time. Furthermore, the extensive network of shallow roots can make it difficult to maintain a healthy lawn or garden plants directly beneath the tree’s canopy due to competition for water and nutrients.
Ash trees are also susceptible to other diseases and pests independent of the EAB, although these are typically less fatal. For instance, Ash Yellows is a systemic disease caused by a phytoplasma, which leads to slow growth, premature fall color, and eventual branch dieback. While not as universally lethal as the EAB, it can significantly reduce the tree’s lifespan and aesthetic appeal.
Strategic Management and Alternatives
For individuals who currently possess mature ash trees, the decision is generally reduced to two primary courses of action: implementing a preventative insecticide treatment program or planning for eventual removal. The choice depends heavily on the tree’s value, health, and size, as well as the local EAB infestation pressure. Untreated trees in infested areas face a near-certain death within a few years.
Preventative treatment involves the use of systemic insecticides applied directly to the trunk or soil. These treatments must typically be reapplied every two to three years to maintain effectiveness, requiring a commitment to long-term chemical maintenance and associated costs. This approach can effectively protect high-value landscape trees but is generally impractical for large forest stands or low-value individuals.
When considering new planting, the current risk level associated with ash trees necessitates turning to suitable alternatives that offer similar landscape benefits without EAB susceptibility. Selecting a species that is not only resistant to EAB but also genetically diverse from ash helps ensure the new addition will not be susceptible to future pest or disease threats. This strategic selection promotes a more resilient and sustainable landscape.
Effective replacement options that replicate the ash tree’s fast growth, upright habit, and strong structure include:
Certain cultivars of maple trees, particularly disease-resistant varieties, which provide excellent shade and fall color.
Oaks, such as the Red and White varieties, which offer strong wood and long-term canopy structure.
Disease-resistant elm cultivars.
Various ironwood or hornbeam species.