Ash trees (Fraxinus) are widely distributed deciduous hardwood species found across North America. Understanding their growth rate is important for landscape planning and forestry management. The annual height and diameter increase is highly variable, depending on the specific species and environmental conditions. Examining typical growth rates under optimal conditions provides a starting point for gauging potential development.
Typical Growth Rates by Ash Species
Ash trees are generally recognized as having a fast to moderate growth rate, though there is a considerable difference between species. The fastest growing of the three main North American species is typically the Green Ash (Fraxinus pennsylvanica). Under favorable conditions and with adequate moisture, young Green Ash trees can gain between two to three feet in height annually. Extremely fast growth has been documented in warmer southern regions, where young, irrigated Green Ash can add six to ten feet in a single year.
White Ash (Fraxinus americana) is a moderate to fast-growing species, generally slower than Green Ash. It typically gains between one and two feet of height annually in suitable sites. Studies in forest plantations show the average height increase ranges from 0.7 to 2.6 feet per year, highlighting the influence of local factors.
The Black Ash (Fraxinus nigra) is the slowest growing of the common ash species, often because of its specialized habitat preference. While sometimes capable of moderate growth on better-drained sites, it usually exhibits a much slower rate overall. Its annual growth increment is often less than one foot, and one study showed an average annual diameter increase of only 3.8 millimeters. Its tendency to grow in wet, sometimes nutrient-poor soils contributes to this reduced rate of development.
Essential Environmental Conditions for Optimal Growth
Achieving the maximum growth rates listed for each ash species depends on meeting their specific environmental needs. All ash species require full sunlight exposure to reach their greatest growth potential. While young White Ash can tolerate some semi-shade in a forest understory, their growth accelerates significantly once they reach the main canopy.
Soil requirements also differ among the species, influencing their success in various locations. White Ash prefers deep, fertile, well-drained soils that retain moisture, thriving in a wide range of soil pH from mildly acidic to alkaline. Green Ash demonstrates remarkable adaptability, tolerating both wet and dry sites, and it performs well in compacted urban soils, including those with a high pH.
Black Ash is strongly tied to wetland habitats, typically growing in areas with poor drainage like floodplains and swamps. The soil must be moist to wet, often consisting of peat or muck. If any ash species experiences prolonged drought or nutrient deficiency, annual growth will be severely limited.
The Limiting Factor: Emerald Ash Borer and Survival
While ash trees can demonstrate substantial annual growth, the long-term survival and sustained development of North American ash species are profoundly affected by the presence of the Emerald Ash Borer (EAB, Agrilus planipennis). The larvae of this invasive beetle feed on the phloem tissue just beneath the bark, disrupting the tree’s ability to transport water and nutrients. This feeding action effectively girdles the tree, which halts all future growth and ultimately leads to death.
The time from initial infestation to mortality is often rapid, dramatically shortening the lifespan and overall growth period of the tree. Mature ash trees can die within six years of infestation, with widespread death across an area often occurring within two to three years of the beetle’s initial detection. Smaller trees and saplings can be killed even faster, sometimes in a single year.
In areas where the EAB is established, sustained healthy growth requires consistent chemical treatment. Without systemic insecticides, nearly all untreated native ash trees will succumb to the infestation. The EAB crisis changes the focus from maximum annual increase to the necessity of protective measures for long-term survival.