True ash trees are all of the Fraxinus genus in the Oleaceae (olive) family of the Lamiales or Mint order.
The Fraxinus genus has 47 to 65 different types of ash trees. Based on fossils found in British Columbia, Canada, they are believed to have evolved about 50 million years ago.
True ash is native to the Northern Hemisphere and widespread throughout Europe, Asia, and North America.
Mountain ash trees have similar leaves but are from a completely unrelated Sorbus genus in the Rosaceae family of the Rosales order. Since they have similar names and superficially look similar, we will also learn to identify a few mountain ash trees.
Over 100 different types of mountain ash trees are also native throughout the northern hemisphere.
While the Emerald Ash Borer has devastated many true ashes, the unrelated mountain ash is immune.
Ash Tree Identification (With Photos)
Identifying Ash Trees by Their Pinnately Compound Leaves
Ash trees, both true and mountain ashes, tend to have compound odd-pinnate leaves.
These leaves may be in opposite pairs at branch nodes or rarely whorled at branch tips in some Fraxinus ashes.
Leaves are arranged singly and alternately at the nodes in Sorbus mountain ashes.
The arrangement of leaves on the branches is an easy way to tell the two types of ash trees apart when flowers or fruits are not visible.
Odd-pinnate or imparipinnate compound leaves are leaves made of three or more leaflets attached to a central stalk known as a rachis that is usually attached to branches or twigs by a leaf stalk known as a petiole.
There are one to many pairs of lateral leaves and one terminal leaf at the tip of the rachis.
Sometimes the leaflets themselves may also have leaf stalks known as petiolules, but other times they are sessile or stalkless. This is a useful tool for identifying the different types of ash trees.
This image of a sumac leaf clearly shows the different parts of an odd-pinnate compound leaf.
True ash trees often have a pulvinus or thickening at the petiole’s base and sometimes the petiolules.
Mountain ash trees often have stipules at the base of their leaves that may be persistent or deciduous. Stipules are small leaf-like appendages usually found in pairs at the base of the true leaf or leaflet.
True ash trees never have stipules, so this is another way they can be differentiated when not in flower or fruit.
Identifying Ash Trees by Their Leaflet Shape
Ash tree leaflets can have many different shapes that can be very helpful in identifying the different types of ash trees. Similar shape names are often also used to describe buds and fruits.
Leaflets may be ovate (egg-shaped), obovate (egg-shaped but widest at the tip instead of the base), lanceolate (like ovate but narrower, with a length-to-width ratio of 3:1 or greater), oblanceolate (like lanceolate but wider at the tip, sometimes referred to as spatulate), elliptic (widest in the middle and narrowing at both ends), or oblong (sides that are parallel and ends that are rounded or obtuse).
Identifying Ash Trees by Their Leaflet Apex or Tip
Ash leaflet tips can have characteristic shapes that can help aid in their identification. Often the tip is acuminate or pointy, and often that pointy tip is long-acuminate, but sometimes it can be short acuminate.
Other tips can be acute (angled but at less than 90°), obtuse (angled at greater than 90°), rounded, cuspidate (a short, stiff tip), or caudate (like long-acuminate but looking like it has a tail-like appendage at the tip).
Identifying Ash Trees by Their Leaflet Base
Ash leaflet bases are less variable but can also be used to help identify the different species.
True ash leaflet bases are often acute or cuneate (angled but at less than 90°), obtuse (angled but at greater than 90°), oblique (asymmetrical – one side is larger or extends further down the petiolule than the other), or decurrent (where the leaf blade extends down the petiolule).
Mountain ash leaflet bases are much less variable than true ashes and tend to be mostly rounded or obtuse but are sometimes acute or oblique.
Identifying Ash Trees by Their Leaflet Margins
Ash leaflet margins are often serrated (coarsely toothed, like a saw). Serrated margins can be coarsely serrated with larger or more widely spaced teeth, finely serrated with small teeth, or occasionally doubly serrated when the teeth then have their own teeth.
Other times margins may be entire (smooth, lacking teeth). Occasionally margins may be crenate when the teeth are more rounded than jagged. Crenulate is when the rounded teeth are very small.
Identifying Ash Trees by Hairs and Other Surface Features
Leaves, leaf veins, petioles, petiolules, twigs, and buds often have surface features that can help identify different ash tree types.
Surfaces may be variously hairy, including puberulent (finely soft short-hairy), pubescent (soft hairy), tomentose (long curly hairs that are matted), villous (long curly hairs that are not matted), hispid (stiff straight hairs), or ciliate (straight hairs along the edge of a leaf, sepal, etc).
Surfaces may also be papillose or not. Papillose are bumps or wart-like protrusions of the surface tissues.
Sometimes surfaces may have scales. Scales are botanically identical to plant hairs, which are not like the animal hairs named after, but actually trichomes. Scales are flattened trichomes that appear on the surfaces of some species. But, since scales do not resemble animal hairs, we refer to them as scales.
Finally, sometimes surfaces may have a glaucous coating. This is a waxy coating excreted by the plants that can easily be rubbed off. It gives surfaces a dull bluish-gray waxy look.
Identifying Ash Trees by Their Winter Leaf Buds
Sometimes the winter leaf buds’ color, size, or shape can be useful in identifying the different types of ash and mountain ash trees.
Most buds are conical in shape but may be broad or narrow. They are often brown, grayish, or reddish-brown in color but occasionally can be black, like the European Ash shown in the photo below.
Mountain ash buds especially may also be viscid (sticky) or not, which can be used to help identify the species.
Ash Trees And Their Gender-Fluid Spectrum of Sexuality
The sexuality of true ashes is actually quite fascinating. Strict gender concepts like “male trees” and “female trees” do not apply to most true ash trees.
Even though many online sources claim ash trees are dioecious, implying separate male and female trees, this is less common than often believed.
Many ash trees could be more correctly called gender-fluid, with their sexuality being more on a spectrum than a black-or-white definition.
Ash trees produce small flowers that are often unisexual with separate male and female flowers, but sometimes they are bisexual, having both male and female reproductive parts.
While true dioecious and bisexual trees do exist, often, trees will have male, female, and bisexual flowers on the same tree in varying proportions.
For example, studies found that a single “male tree” might actually have 63% male flowers, 36% bisexual flowers (of which 61% were functionally female and 25% were functionally bisexual), and 1% female flowers.
Moreover, their predominant gender can change from year to year, so it may be mostly male one year but mostly female another year.
Hence gender-fluid spectrum is a more accurate description.
Mountain ashes are very different from true ashes. As part of the rose family, they have functionally bisexual flowers with both male and female reproductive organs in the same flower. Many mountain ash plants are even self-compatible and can fertilize themselves, while others are self-incompatible.
Identifying True Ash Trees by Their Flowers
Like much of the Oleaceae family, true ash trees have “4-merous” flowers. These are flowers whose parts are in fours (or twos).
The calyx is partially joined and usually appears as four small teeth at the base of the flower. Often they are very small, and sometimes they are absent.
Petals are often absent in true ashes. When present, they may be yellowish or white, partially joined creating a four-lobed corolla, or divided all the way to the base. Sometimes there are four petals, and occasionally there are only two. Their presence and number can be very useful in identifying certain types of ash trees.
In male and bisexual flowers, there are almost always two stamens that are typically inserted at the base of the corolla lobes. They usually have short filaments, but often only the anthers are visible. Some species only have one stamen, which is useful in identifying them.
Female and bisexual flowers have an ovary with two locules or chambers, each with two seeds, but you must cut the flower open to see those features. Above the ovary is one short style and a single, mostly 2-cleft stigma. You can see the two divided lobes of the stigmas in the pictures below.
Identifying Mountain Ash Trees by Their Flowers
Mountain Ash flowers from the rose family have bisexual 5-merous flowers or flower parts in fives.
They have five petals that are free from each other and may or may not be clawed at the base. They also have various characteristic sizes and shapes that can be used to identify the species. Five sepals may be tiny to large but are always present.
Each flower also contains 15 – 25 (-44) stamens in 2 – 3 whorls of unequal lengths, 2 – 5 styles, and ovaries with 2 – 5 locules, each with 2 – 3(4) seeds though one is usually abortive.
The number and color of anthers and styles are also useful tools in identifying the different types of mountain ash trees.
Identifying Ash Trees by Their Fruits
Fraxinus species are slightly unique in the Oleaceae family for producing samaras, most others produce berries or drupes. Samaras are winged fruits.
Ash trees do not have helicopter-like samaras like maple trees. Instead, they have single-seeded samaras, often called “ash keys”.
The length of the samaras, how far the wing extends past the seed, and whether it appears twisted are useful tools in helping to identify true ash trees.
Mountain Ash trees, being from the Rosaceae family, produce small berry-like pomes. A pome is an accessory fruit where the fleshy fruit part is derived from floral tissues like a receptacle or hypanthium rather than the ovary itself. An apple is an example of a pome.
Mountain Ash fruits are botanically very similar to an apple, but on a much smaller scale and look much more like little berries and are sometimes incorrectly called berries or drupes.
These tiny pomes are often orange or red when ripe and are a favorite food source of birds, especially in winter. The color and size of the pomes can be useful in helping to identify the different types of mountain ash.
Identifying Ash Trees by Their Bark
The color and patterns of ash tree bark can also be used to help identify the different types of ash trees.
Their bark always starts out smooth when young. As it matures, it may remain smooth or develop shallow grooves, deep diamond-shaped grooves, rectangular plates that may or may not be scaly or flaky, or cross-checked plates.
Mountain Ash bark usually remains mostly smooth when mature but often develops horizontal lenticels on its surface. Lenticels are raised pores on bark surfaces that allow for gas exchange with the atmosphere.
18 Different Types of Ash and Mountain Ash Trees & Their Identifying Features
1. Fragrant Ash (Fraxinus cuspidata)
Fragrant Ash is by far my favorite ash tree. It is a beautiful, low-maintenance, often multi-trunked shrub or small tree with a rounded crown and gorgeous showy, fragrant flowers that bloom in late spring.
It is easy to grow and works great in small gardens and will even grow in pots on a patio where the flowers can be appreciated.
It grows wild on rocky slopes, cliffs, and desert foothills, tolerating prolonged droughts and cold (but not frigid) winters.
It will grow in any soil type, from slightly acidic to slightly alkaline and sandy to even clay soils, although it does prefer good drainage.
It can be grown in full sun or partial shade.
Pollinating insects and birds are attracted to the fragrant blossoms.
So far, it has not been strongly affected by the Emerald Ash Borer, but it is known to be susceptible to it.
Identifying Features of the Fragrant Ash
Fragrant Ash is a usually multi-trunked shrub or small tree with slender, hairless branches and smooth to slightly cross-checked bark.
Leaf buds are dark reddish-brown.
Their deciduous compound leaves are about 7” long and odd-pinnate with 3 – 9 leaflets.
Leaflets are ovate to oblanceolate or lanceolate, thin, light shiny green, and 1.4 – 2.8” long. In the fall, they turn yellow.
Leaflet margins are entire to coarsely toothed, both surfaces may be hairless or finely hispid, the lower surface is often dotted with scales, and the tip is long-acuminate to cuspidate.
Fragrant flowers open with new leaves in spring with four large linear white petals that are united at their base into a tube. The entire flower can be from 1 – 3” long.
Fruits are oblong-obovate to lanceolate samaras that hang in clusters.
Often Confused With: Fragrant Ash is mostly confused with Velvet Ash with its similar-sized and colored leaves, but Velvet Ash leaf surfaces are sometimes puberulent and lack the visible scales on the lower surfaces, the bark is rough-scaly, and its flowers are apetalous and inconspicuous rather than showy and fragrant. It is also sometimes confused with Mexican Ash (Fraxinus berlandieriana), but that one also has apetalous flowers, prominent grooves in its bark, and its fruits are larger.
Other Common Names: None
Native Area: Southwestern USA (Texas, New Mexico, Arizona, Nevada) and northern Mexico (Nuevo León, Coahuila, Chihuahua, Tamaulipas)
USDA Growing Zones: 5 – 9
Average Size at Maturity: 8 – 15 ft (to 20 ft) tall, 8 – 12 ft spread
2. Green Ash (Fraxinus pennsylvanica)
Green Ash is a gorgeous medium to large-sized tree with a wide native range across central and eastern North America.
It is easy to grow, can tolerate various soil conditions, and is tolerant of pollution and road salts in urban areas.
It prefers to grow in moist soils in full sun.
In nature, it is often found growing in moist or wet forests.
Unfortunately, this lovely tree has been severely impacted by the Emerald Ash Borer and is not recommended for planting in affected areas unless a resistant cultivar is chosen.
This tree is now Critically Endangered in the wild.
Fortunately, a very small percentage of Green Ash has survived the infestation, according to research done at Penn State. These resistant trees could potentially be used to repopulate the species.
Identifying Features of the Green Ash
Green Ash is a medium to tall tree with plated flaky bark or diamond-shaped grooves.
It has odd-pinnate deciduous compound leaves with 7 (5 – 9) leaflets that are lanceolate or lanceolate-ovate to oblong or elliptic with acuminate to obtuse or acute tips.
Leaflet margins are serrate to crenulate or almost entire. Bases are broadly cuneate, somewhat oblique, and usually decurrent onto the short petiolule, though sometimes they are almost sessile.
Twigs and leaves are densely pubescent to hairless; leaf undersides may have hispid hairs along the midvein.
The terminal bud is acute and taller than wide.
Flowers usually have only one stamen or one style, a tubular calyx, and are apetalous.
Fruits are linear to spatulate samaras, the wing extending to about the middle, and its free part is shorter than the body itself, and a very small calyx may persist.
Often Confused With: Green Ash is mostly confused with White Ash, but they can be differentiated by White Ash’s leaflets that are oblong to ovate or obovate with tips that are usually abruptly acuminate, bases that are typically not decurrent, lower surfaces that are papillose, and the wings on its fruits are longer than the body itself rather than shorter. Sometimes it is confused with European Ash, but that one has 7 – 13 elliptic sessile leaflets, or Black Ash, which has 7 – 11 sessile leaflets with very serrated margins.
Other Common Names: American Ash, Canadian Ash, Red Ash, Water Ash, Swamp Ash
Native Area: North America from Alberta east to Nova Scotia in Canada all south through Montana to Texas and east to Florida and the Atlantic states of the USA
USDA Growing Zones: 3 – 9
Average Size at Maturity: 50 – 70 ft tall, 35 – 45 ft spread
Some Cultivars Available:
3. White Ash (Fraxinus americana)
White Ash is a large native North American Ash tree with a pyramidal crown that becomes rounded with age.
It grows naturally in moist, but not wet, forests. It prefers full sun and will grow in most soil types.
Its deciduous leaves have a lovely purplish-yellow fall color.
Sadly, it is highly susceptible to the Emerald Ash Borer, and its population has been devastated.
As a result, it is listed as Critically Endangered, and its population is declining.
It is no longer recommended for planting unless a resistant cultivar is chosen.
Identifying Features of the White Ash
White Ash is a tall tree with a rounded crown and gray bark with fine diamond-shaped grooves.
Its deciduous compound leaves are odd-pinnate with 7 (5 – 9) leaflets on petiolules. Leaflets are oblong to ovate or obovate with usually abruptly acuminate tips.
Leaflet margins are crenulate or occasionally entire. The upper surfaces are dark green, while the lower surfaces are pale green and papillose.
Twigs and leaves are mostly hairless.
The terminal bud is obtuse and wider than tall.
Trees are mostly dioecious, and flowers lack petals and have only a tiny four-lobed calyx.
Male flowers have two stamens with linear, apiculate (pointy), often purple or reddish anthers. Female flowers have a single style.
Fruits are linear to oblanceolate samaras 1.2 – 2” long, with the wing extending a third of the length of the rounded body and the free part above the body longer than the body itself.
Often Confused With: White Ash is mostly confused with Green Ash which has leaflets that are lanceolate or lanceolate-ovate to oblong or elliptic with bases that are often decurrent and lower surfaces that may have hispid hairs along the midvein but are not papillose, buds that are taller than wide, and fruits that have wings whose free part is shorter than the body itself. Occasionally it is mistaken for Black Ash which has 7 – 11 sessile leaflets with very serrated margins.
Other Common Names: Biltmore Ash, Biltmore White Ash
Native Area: Eastern North America from southern Ontario east to Nova Scotia, Canada, and in the USA from Minnesota southwest to eastern and central Texas plus all states east of that Florida north to Maine
USDA Growing Zones: 3 – 9
Average Size at Maturity: 60 – 80 ft tall, 50 – 80 ft spread
Some Cultivars Available:
- Autumn Purple Ash Tree Fraxinus americana ‘Autumn Purple’ is tolerant of various soil types and mild drought. It is a full-sized tree with beautiful red and purple fall colors. Image via Fast-Growing-Trees
- Autumn Blaze Ash Fraxinus americana ‘Autumn Blaze’ is the first White Ash developed specifically for the prairies in zones 3 – 8. The rounded crown displays showy purple fall color. Resistant to Emerald Ash Borer. Image via Nature Hills
4. Blue Ash (Fraxinus quadrangulata)
Blue Ash is an uncommon tree with a fairly narrow native range, mostly in the midwestern USA.
It gets its name from the gelatinous inner bark that turns blue upon contact with the air. Early Americans used to use it as a source of dye.
The fall color is not as showy as others, becoming grayish to dull yellow.
It grows best in full sun in most soil types.
It is often recommended for dry sites but will also do well in medium-wet but not constantly wet areas.
It makes a great shade or street tree that tolerates pollution and road salts.
It appears to have a higher resistance to the Emerald Ash Borer than most North American ashes, with about a 60 – 70% survival rate.
But it is not a common tree, and this, combined with some susceptibility, has it listed as Critically Endangered.
Identifying Features of the Blue Ash
Blue Ash is a medium to tall tree with a rounded to irregular crown and gray bark that develops irregular plates as it matures.
It has distinctive sharply 4-angled or narrowly 4-winged corky twigs that help to identify it quickly.
It has deciduous odd-pinnate compound leaves with 7 – 11 dark green 4 – 5” long leaflets, usually lanceolate with long-acuminate tips. Leaf bases are broadly cuneate to almost rounded and usually oblique at the petiolule base.
It has apetalous bisexual purplish flowers that appear in the spring before the leaves. Its anthers are obtuse or cleft at the tip.
Fruits are flat, elliptic to narrowly oblong-obovate samaras 1 – 2” long, usually emarginate (having a notch at the tip), the wing extending nearly or to the base.
Often Confused With: Blue Ash is easily recognizable by its 4-angled or winged twigs and its bisexual flowers. But it is mostly confused with White Ash which usually has 7(5 – 9) leaflets that are oblong to ovate or obovate with usually abruptly acuminate tips and papillose lower surfaces; it also has unisexual flowers. Sometimes it is confused with Green Ash, but it usually has only unisexual flowers, and its 7 (5 – 9) leaflets often have decurrent bases.
Other Common Names: Winged Ash, Frêne bleu (French)
Native Area: Narrow range in the midwestern USA from Oklahoma to Michigan and south through central Kentucky and Tennessee, but mostly in Missouri. Isolated populations also occur in Alabama, southern Ontario (Canada), and the Appalachian Mountains
USDA Growing Zones: 4 – 7
Average Size at Maturity: 50 – 80 ft tall, 35 – 60 ft spread
5. Black Ash (Fraxinus nigra)
Black Ash is an interesting tree with a rich cultural history. The Wabanaki, and later pioneers, used the pliable branches to weave baskets, and the tree plays a prominent role in several native American creation stories.
It grows well in cold and wet locations and is often found in swamps and wetlands.
It prefers to grow in full sun.
It has a shallow root system compared to other ash trees, which makes it susceptible to windthrow and often creates a leaning tree.
Wildlife are frequent visitors, with birds and animals feeding on their winged seeds and deer and moose feeding on leaves and branches.
Unfortunately, this is one of the North American ash trees that are the most susceptible to the Emerald Ash Borer, with only about a 1% survival rate, so it is no longer recommended for planting.
It is also listed as Critically Endangered.
Identifying Features of the Black Ash
Black Ash is usually a medium-sized tree but can grow quite tall if conditions allow it. It has a very slender trunk that rarely gets more than 2 ft wide and has no branches for much of its length.
Its mostly rounded twigs are hairless.
The gray bark becomes soft and spongy as it matures with shallow grooves, often giving it a flaky appearance.
It has deciduous odd-pinnate compound leaves with 7 – 11 sessile leaflets that are lanceolate to oblong with long-acuminate tips and broadly cuneate bases.
Leaflet margins are usually very serrated but can be finely serrated.
Trees can have male, female, and bisexual flowers on the same or different trees.
Samaras are flat, lanceolate to oblanceolate, 1 – 1.6” long, with a rounded to emarginate (notched) wing, extending nearly or to the base, without a persistent calyx.
Often Confused With: Black Ash is confused with Green Ash and White Ash, but both of those have thicker trunks, and usually, only seven leaflets with petiolules or may be subsessile but are never fully sessile, and their leaflet margins are typically entire or crenulate rather than very serrated. White Ash margins are sometimes serrated but never very serrated.
Other Common Names: Swamp Ash, Basket Ash, Brown Ash, Hoop Ash, Water Ash
Native Area: Northeastern North America from Manitoba east to Newfoundland in Canada, Minnesota south to Iowa, and east to Maine south to New York in the USA
USDA Growing Zones: 2 – 6
Average Size at Maturity: 40 – 70 ft (to 100 ft) tall, 30 – 60 ft spread
6. California Ash (Fraxinus dipetala)
California Ash is a shrub or small tree that appears different from most other ashes with its smaller and fewer leaflets and its fragrant flowers with two white petals.
It is a very drought-tolerant shrub or tree, and once established, it will do well in areas without access to water.
It grows best in full sun from 325 – 4265 ft above sea level but also tolerates partial shade.
It grows well in most soil types, from acidic to alkaline, but prefers good drainage.
Its leaves often turn bright golden yellow in the fall.
Its susceptibility to the Emerald Ash Borer is still unknown as the pest has yet to reach its native range. But it is expected to reach the west coast soon, so time will tell. For now, its population is still doing well.
Identifying Features of the California Ash
California Ash is a large shrub or small tree that is often multi-trunked and has rounded or four-angled stems.
It has odd-pinnate compound leaves that are 2 – 7.5” long with 3 – 7 (9) leaflets.
Leaflets are light to dark green, 0.4 – 2.75” long, with rounded tips and serrated margins.
Flowers hang in fluffy clusters and are unusually bisexual and have two short white two-lobed sweet-scented petals.
The fruit is a flat samara 0.8 – 1.25” long and hangs in clusters.
Often Confused With: California Ash’s fragrant two-petaled flowers make it hard to mistake for other ash trees. It is mostly confused with the Oregon Ash (Fraxinus latifolia), which is a larger tree with lighter green leaflets that are larger and wider than the California Ash. It is also confused with Blue Elder (Sambucus cerulea) with its odd-pinnate leaves, but that can easily be differentiated by its dense flat-topped inflorescences of white flowers followed by blue berry-like drupes.
Other Common Names: Two-Petal Ash, Foothills Ash
Native Area: Southwestern USA in California, Arizona, Utah, Nevada, plus Baja California in northwestern Mexico
USDA Growing Zones: 7 – 10
Average Size at Maturity: 10 – 25 ft tall, 10 – 15 ft spread
7. Carolina Ash (Fraxinus caroliniana)
The Carolina Ash is a small to medium-sized wetland tree with pretty glossy green leaves.
It is found mostly in swamps and bottomlands as an understorey tree, mainly along the coastal plain of the southeastern USA and Cuba. It does not tolerate brackish water or salt spray.
Unlike many ash trees, this one does well in full sun or quite shady conditions.
It helps mitigate flood damage by stabilizing wetlands and slowing the surface flow, allowing time for the water and sediments to settle.
The Emerald Ash Borer is now spreading south and east into its range and has started infesting this species that, until 2013 or so, had been outside of its range.
It is now considered Endangered in its native range, and the Cuban subspecies is Vulnerable.
Identifying Features of the Carolina Ash
Carolina Ash is a small to medium-sized tree often enlarged at the base and leaning, with a rounded to narrow crown and mostly rounded twigs that are finely pubescent to hairless.
The bark is grayish with irregular to somewhat rectangular scaly ridges when mature.
It has odd-pinnate deciduous glossy green leaves 7 – 12” long with 5 – 7 leaflets with petiolules. Leaflets are lanceolate to elliptic with an abruptly acuminate to obtuse tip and coarsely serrated to entire margins.
Upper leaflet surfaces are puberulent with scattered scales and hispid hairs along the midrib, the lower surface is tomentose, pilose (long pubescent), or puberulent, smooth along the veins.
Samaras are flat, lanceolate to elliptic, 1.4 – 2” long, broader than most ashes, with a minute calyx and a wing extending to or nearly to the base.
Often Confused With: Carolina Ash is mostly confused with Green Ash, but its 7(5 – 9) leaflets are often oblique at the base and decurrent, they may have hispid hairs along the midvein on the lower surface, and their margins may be crenulate or serrated. Green Ash typically also has narrower samaras. Sometimes it’s confused with Pumpkin Ash which also may have a swollen base when growing in wet conditions, but it has leaflets with conspicuously longer petiolules, plus thick branches and hairy twigs.
Other Common Names: Florida Ash, Pop Ash, Poppy Ash, Swamp Ash, Water Ash
Native Area: Southern USA along the Atlantic coast from Virginia south to Florida and west to Texas, with a subspecies found in Cuba
USDA Growing Zones: 7 – 10
Average Size at Maturity: 25 – 50 ft tall, 10 – 30 ft spread
8. European Ash (Fraxinus excelsior)
The European Ash is a tall ash tree with a broad crown that is often wider than it is tall.
While many cultivars have a yellow color in the fall, the type species tend to drop their leaves while they are still green.
European Ash is reportedly less attractive to the Emerald Ash Borer than Black, Green, and White Ashes.
New studies have shown that while it is no more resistant to the initial attack, it appears better able to fend off the insect as it matures, restricting its development and reducing its impact, resulting in a higher survival rate.
It is best grown in moist, rich, well-drained loams in full sun. It does best in areas with mild summers and will do poorly in hot or dry conditions.
It is Near Threatened in its native range, and its population is decreasing.
Identifying Features of the European Ash
European Ash is a large deciduous tree with a thick trunk of 6.6 ft (to 11 ft) wide with smooth pale gray bark that becomes thickly grooved when mature.
Shoots are stout greenish-gray, and the winter buds are jet black.
Odd-pinnate compound leaves are 7.9 – 13.8” long with 7 – 13 elliptic sessile leaflets that are 1.2 – 4.7” long and have coarsely serrated margins.
Trees may be dioecious or have both male and female unisexual flowers, or switch from male to female from one year to the next.
Small flowers appear in short panicles in spring before the leaves open. They lack petals and sepals.
Female flowers are a bit larger than male flowers and have dark purple stigmas.
The fruit is a 1 – 1.75” long samara that hangs in bunches.
Often Confused With: European Ash is easily identified by its jet-black buds compared to other ash trees that are grayish or brownish but never black. It is mostly confused with Green Ash but can usually be distinguished by the latter having leaflets with short petiolules or subsessile but not sessile and margins that are not coarsely serrated. Sometimes it is confused with Narrow Leaved Ash, but that one has more slender leaflets and cross-checked rather than grooved mature bark.
Other Common Names: Common Ash, Ash
Native Area: Most of the European mainland, plus Britain and Ireland, and east into western Asia
USDA Growing Zones: 5 – 8
Average Size at Maturity: 60 – 80 ft (to 140 ft) tall, 50 – 80 ft spread
9. Little Leaf Ash (Fraxinus greggii)
Little Leaf or Gregg’s Ash is a large shrub or small tree that is drought-tolerant once established and does well in a container.
It makes a nice patio tree in large pots and also makes a nice compact shade tree or privacy screen.
It does well in full sun in any well-draining soil and can tolerate some partial shade.
In nature, it grows along washes and rocky slopes in gravelly soil at 2500 – 7000 ft above sea level.
So far, its native range has not yet been impacted by the Emerald Ash Borer, but it could soon be affected as the pest spreads west and south.
Its resistance or susceptibility is unknown, but its population is still doing well for now.
Identifying Features of the Little Leaf Ash
Little Leaf Ash is a multi-trunk shrub or small tree with smooth, gray to brownish-gray bark that darkens when mature but typically remains mostly smooth.
It has odd-pinnate bright green leaves with usually three but up to seven small, thick, leathery, lanceolate leaflets. They are semi-evergreen, often only shedding their leaves in the spring right as the new leaves emerge.
Flowers are small and inconspicuous, with separate male and female flowers that are usually on the same plant (monoecious), but the male flowers appear before the female flowers to avoid self-pollinating.
Flowers lack petals but have green sepals. Male flowers have purple anthers, and female flowers have yellow stigmas and ovaries that turn brown as they mature.
Fruits are flat, dark, and winged and persist on the tree for some time.
Often Confused With: Little Leaf Ash is rarely confused with other ash trees because of its small, leathery, semi-evergreen leaflets that are unique in the genus. It is mostly confused with Barreta (Helietta parvifolia), which grows to similar sizes and also has odd-pinnate leathery leaflets, but its terminal leaflet is usually larger and obovate or oblanceolate, and its flowers have creamy white petals.
Other Common Names: Gregg’s Ash, Mexican Ash, Dogleg Ash, or in Spanish Escobilla, Barreta, China, Fresno
Native Area: Southern Arizona, southern New Mexico, western Texas in the USA, and northeastern and central Mexico in Coahuila, Nuevo León, Zacatecas, Tamaulipas
USDA Growing Zones: 7 – 10
Average Size at Maturity: 10 – 20 ft tall, 8 – 15 ft spread
10. Manna Ash (Fraxinus ornus)
The Manna Ash is a lovely flowering ash tree with beautiful fragrant flowers that bloom in May.
Its name comes from the food described in the Bible because of its sweet sap extract that contains mannitol and mannose sugars.
Its deciduous leaves turn yellow to purplish in fall.
Like other Eurasian ash trees, this species may be more resistant to Emerald Ash Borer.
It prefers to grow in full sun but does not like intense heat, so if this describes your area, be sure to plant it where it gets some afternoon shade.
It has been introduced worldwide in many countries (so far, not yet in North America) and is sometimes considered invasive.
Identifying Features of the Manna Ash
Manna Ash is a medium-sized tree with a trunk up to 3.5 ft wide. It has an oval to rounded irregular crown, and its bark is dark gray and remains smooth even when mature.
Leaf buds are pale pinkish-brown to gray-brown and have a gray pubescence on them.
It has odd-pinnate compound leaves 7.9 – 12” long with 5 – 9 leaflets that are broadly ovate with a finely serrated and wavy margin and acuminate tips. Leaflets have short petiolules.
Flowers appear in dense panicles 3.9 – 7.9” long after the new leaves appear. Each flower has four slender white petals about ¼” long.
Fruits are slender samaras 0.6 – 1” long.
Often Confused With: Manna Ash is fairly distinctive with its smooth bark and showy flowers. It is mostly confused with European Ash, which has thickly grooved bark and apetalous flowers. Fragrant Ash also has showy four-petaled flowers, but it is usually a smaller tree with smaller leaves, and its flowers are much longer (up to 3”).
Other Common Names: Flowering Ash, South European Ash, Southern European Flowering Ash
Native Area: Throughout southern Europe into western Asia, naturalized elsewhere now
USDA Growing Zones: 6(5) – 9
Average Size at Maturity: 40 – 50 ft (to 85 ft) tall, 30 – 50 ft spread
11. Narrow-Leaf Ash (Fraxinus angustifolia)
Narrow-Leaf Ash is sometimes called Fraxinus oxycarpa, but plant authorities say that’s a synonym of Fraxinus angustifolia.
It is a medium to large-sized tree that grows well in acidic soils and urban conditions and requires less water than most ash trees.
This ash may also resist the Emerald Ash Borer more than most North American species.
Like most ash trees, this one also does best in full sun.
It has become invasive in parts of Australia and has the potential to invade other areas, so it should be planted with caution.
Identifying Features of the Narrow-Leaf Ash
Narrow-Leaf Ash is a medium or large-sized tree with a thick trunk up to 5 ft wide.
Its bark is smooth and pale gray when young but becomes grooved and cross-checked when mature.
Leaf buds are pale brown.
The odd-pinnate compound leaves are 5.9 – 9.8” long and may be arranged in opposite pairs or whorls of three at the nodes on the branches.
Leaves have 3 – 13 leaflets 1.2 – 3.15” long that are distinctively slender (0.4 – 0.6” wide) compared to other ashes.
Flowers are produced in early spring in inflorescences which can be male, bisexual, or mixed male and bisexual. All trees contain both and are functionally bisexual.
Fruits are 1.2 – 1.6” long samaras, with the seed about half the length and the pale brown wing half the length.
Often Confused With: Narrow Leaf Ash is quite similar to the related European Ash, but the latter has wider leaflets, grooved rather than cross-checked bark, jet-black rather than pale brown buds, and its leaves are always opposite and never in whorls of three.
Other Common Names: Narrow-Leaved Ash, Narrow Leaf Ash, Desert Ash, Golden Stem Ash, Phoenix Ash
Native Area: Central and southern Europe, northwest Africa, southwest Asia.
USDA Growing Zones: 5 – 9
Average Size at Maturity: 50 – 80 ft tall, 30 – 40 ft spread
12. Pumpkin Ash (Fraxinus profunda)
Pumpkin Ash gets its name from its trunk, which can swell like a pumpkin, especially when growing in wet soils.
It is found naturally in full sun in wet, swampy soils, often growing in swamps alongside Bald Cypress.
Unfortunately, this rare tree has become even rarer due to its high susceptibility to the Emerald Ash Borer. It is not recommended for planting if you live in an infected area.
It is currently listed as Critically Endangered due to the Emerald Ash Borer infestation.
Identifying Features of the Pumpkin Ash
Pumpkin Ash is a tall tree with a broadly rounded crown, thick branches, and hairy twigs.
Its gray bark develops characteristic diamond-shaped grooves as it matures.
It has odd-pinnate compound leaves with 7 (5 – 9) leaflets that are lanceolate to oblong or elliptic with long-acuminate tips and broadly cuneate to rounded and often oblique bases on conspicuous wingless petiolules up to 0.6” long.
Leaflet margins are entire or almost entire, and the lower leaf surfaces are puberulent to finely tomentose with scattered scales and hispid hairs along veins. The upper surface may be puberulent, with scattered scales, glands, and hispid hairs along veins.
Fruits are linear-oblong to spatulate, 1.6 – 3” long, with the wing extending at least to the middle of the rounded body. There is a short persistent calyx.
Often Confused With: Pumpkin Ash is mostly confused with White Ash, which has leaflets with shorter petiolules, papillose lower surfaces, and margins that are usually crenulate or only occasionally entire. Sometimes it is confused with Green Ash, but that one also has shorter petiolules, leaf bases that are often decurrent, and margins that are crenulate to serrated or rarely almost entire.
Other Common Names: Red Ash, Swell-Butt Ash
Native Area: Scattered populations in eastern North America from Indiana southeast to Maryland, south to northern Florida, and east to southern Louisiana, plus an isolated population in southern Ontario, Canada
USDA Growing Zones: 5 – 9
Average Size at Maturity: 60 – 80 ft (to 130 ft) tall, 30 – 50 ft spread
13. Velvet Ash (Fraxinus velutina)
Velvet Ash is a drought-tolerant ash that does well in any well-drained soil but can also grow in wet soil.
It can be grown in clay, sand, loam, and acidic or alkaline soils.
It prefers to grow in full sun but can scorch in the desert sun if it does not have a full canopy. It could be planted with other trees to prevent this.
It is tolerant of urban conditions and is often grown as a street and shade tree and also for its lovely yellow fall color.
It gets its name from its new shoots that are velvety and from its new leaves that feel soft and velvety in the spring just after they emerge.
It has recently started being hit with the Emerald Ash Borer and is susceptible to it, so check your area to see if it is a problem there before planting it.
Identifying Features of the Velvet Ash
Velvet Ash is a highly variable species that typically grows as a small tree with an irregularly rounded crown, a narrow trunk, and gray-brown bark that is rough-scaly and grooved.
New shoots emerge velvety-puberulent.
It has odd-pinnate compound deciduous leaves 3.9 – 9.8” long with 5 – 7 (3) leaflets 1.6” long or longer on long petiolules.
Leaflet margins are entire or finely serrated. Lower surfaces may be finely coarse-hairy, puberulent velvety hairy, or hairless. The upper surface usually becomes hairless.
Flowers appear in tight clusters of inconspicuous apetalous green or yellowish-green, mostly unisexual flowers in late winter just before or just after leaf emergence.
Fruits are 0.6 – 1.2” long samaras.
Often Confused With: Velvet Ash is mostly confused with Green Ash, but that one often has diamond-shaped grooved bark and usually seven leaflets that often have decurrent bases and shorter petiolules and margins that may be crenulate, serrated, or almost entire.
Other Common Names: Arizona Ash, Modesto Ash, Desert Ash, Leatherleaf Ash, Smooth Ash, Standley Ash, Toumey Ash, Fantex Ash, Fresno (Spanish)
Native Area: Southwestern North America from southern California east to west Texas in the USA, plus northern Baja California east to Coahuila, Nuevo León in northern Mexico.
USDA Growing Zones: 6 – 11
Average Size at Maturity: 20 – 50 ft tall, 20 – 60 ft spread
Some Cultivars Available:
- Modesto Ash Fraxinus velutina ‘Modesto’ is more compact than the type species or other cultivars, with a narrower crown. It grows in alkaline soils, tolerates partial shade, and has the same velvety leaves with spectacular yellow fall color. Image via Nature Hills.
- Fan Tex Ash Fraxinus velutina ‘Fan Tex’ does well in zones 6 – 9, has a symmetrically rounded canopy, tolerates hot, dry climates and alkaline soils very well, and shiny green leaves turn bright yellow in the fall. Image via Nature Hills.
14. Manchurian Ash (Fraxinus mandshurica)
Manchurian Ash has become popular in the last decade as a landscape tree because it has shown good resistance to the Emerald Ash Borer.
Research is being done to cross this species with some North American species that the beetle has hit the hardest.
Its compound leaves turn a lovely shade of yellow in the fall.
Like most ash trees, it prefers moist soils in full sun.
It is highly tolerant of urban pollution and will grow well in any city environment or as a landscape or street tree in moist areas.
However, it does not do well in oceanic climates where it tends to leaf too early and suffer frost damage.
It is not listed on any invasive species databases worldwide.
Identifying Features of the Manchurian Ash
Manchurian Ash are medium to large-sized trees with oval to open crowns and distinctly 4-angled hairless twigs.
Its smooth gray bark becomes only slightly grooved when mature.
Its odd-pinnate leaves are 9.8 – 15.8” long with long petioles and ridged rachis.
There are 7 – 11(13) oblong to ovate-oblong papery leaflets 2 – 7.9” long that are subsessile or on short petiolules whose base may be brown tomentose.
Leaflets have finely serrated margins and are hairless or sparsely white hairy above and tomentose along the veins, especially at the midrib base. Leaflet bases are cuneate to obtuse, slightly oblique, and tips are acuminate to caudate.
Inflorescences are 5.9 – 7.9” panicles of unisexual and bisexual flowers lacking petals and calyxes and appearing before the leaves.
Samaras are oblong to obovate-lanceolate, 1.2 – 1.6” long, winged to the middle or base of the seed, and appear twisted.
Often Confused With: Manchurian Ash is mostly confused with Chinese Ash (Fraxinus chinensis), but that one typically only has 3 – 7(9) leaflets, and its apetalous flowers do have a calyx. Blue Ash also has distinctly 4-angled twigs but longer petiolules, leaflets with long-acuminate tips, only bisexual flowers, and samaras that are typically notched (emarginate) at the tips.
Other Common Names: Japanese Ash
Native Area: Northeast Asia, Japan
USDA Growing Zones: 3 – 6
Average Size at Maturity: 40 – 50 ft (to 100 ft) tall, 20 – 25 ft spread
15. Texas Ash (Fraxinus albicans)
Texas Ash is quite similar to White Ash but is a smaller tree with smaller leaves. In the past, it was sometimes considered a subspecies of White Ash.
It is sometimes referred to as Fraxinus texensis, but plant authorities report that name as a synonym of Fraxinus albicans.
In its natural habitat, it is found on dry, rocky slopes, often over limestone.
It is an easy-to-grow, drought-tolerant, long-lived tree that grows in any well-drained soil in full sun.
It is Near Threatened in its native habitat, where it is uncommon and has a narrow range. Like most North American ashes, it is susceptible to damage by the Emerald Ash Borer, which has recently encroached into its native range.
Identifying Features of the Texas Ash
Texas Ash is a small deciduous tree with a narrow short trunk about 1 foot wide with a densely branched, broadly rounded crown.
It has odd-pinnate compound leaves 5.1 – 7.9” long with usually five rounded-ovate to obovate, oblong-ovate, or elliptic 1.2 – 3” long leaflets with abruptly acute to rounded tips.
Flowers are purple to reddish and produced in small clusters in the spring before the leaves appear. It produces unisexual flowers on separate trees and is dioecious.
Samaras are 0.6 – 1.4” long with an apical wing that is often pinkish in color.
Often Confused With: Texas Ash is mostly confused with White Ash but can be differentiated from it by its smaller leaves with smaller, much more rounded leaflets and smaller samaras. White Ash also grows in more mesic habitats, while Texas Ash grows in drier upland sites.
Other Common Names: Texas White Ash
Native Area: Eastern Texas and southern Oklahoma in the USA, south through northern Mexico to Durango, Mexico
USDA Growing Zones: 5 – 9
Average Size at Maturity: 30 – 40 ft tall, 20 – 35 ft spread
16. American Mountain Ash (Sorbus americana)
American Mountain Ash is, as the name implies, a tree that grows well in mountainous areas, particularly at the southern end of its range, where it does not tolerate excessive summer heat.
It does best in moist, humus-rich, slightly acidic, well-drained soils in full sun but can also tolerate a little shade.
Mountain Ashes are actually not at all related to Ash trees, but they do have very similar-looking leaves but can quickly be differentiated by their alternate rather than opposite arrangement.
They are lovely small shade and accent trees with abundant beautiful showy white flowers and attractive berry-like fruits that birds love, especially in winter.
Unrelated to true Ash trees, they are not susceptible to the Emerald Ash Borer.
They are, however, sometimes prone to bacterial blight, scab, rust, and scale.
Deer like to browse on their foliage.
Identifying Features of the American Mountain Ash
American Mountain Ash is a large shrub or small tree with one or multiple trunks with gray to bronze bark.
Leaf buds are green to purple, shiny, viscous (sticky), and hairless or rufous-hairy along scale margins and tip.
Compound leaves are alternately arranged and odd-pinnate, with stipules that fall off early on.
They have 11 – 17 dull green to yellowish-green lanceolate to oblong-lanceolate leaflets that are at least three times longer than wide.
Leaflet margins are fine to coarsely serrated either all around or only on their top half and entire below. Tips are acuminate to long-acuminate.
Flowers appear in 125 – 400-flowered, flat-topped to rounded panicles 2.4 – 5.9” wide.
Flowers are about ⅓” wide with small sepals and five small white rounded to obovate petals, 14 – 20 stamens, and 3 – 4 styles.
Fruits are bright red to orange-red, not glaucous, mostly rounded berry-like pomes appearing in clusters.
Often Confused With: American Mountain Ash is mostly confused with European Mountain Ash which has 9 – 15 serrated flat medium-green leaflets with acute to obtuse tips and villous hairs on its lower surfaces and on its bud scales and twigs. European Mountain Ash also has inflorescences with fewer flowers and slightly larger fruits.
Other Common Names: American Rowan, American Rowan Tree, Mountain-Ash
Native Area: Northeastern North America Ontario east to Newfoundland, Canada, Minnesota, Wisconsin, and northern Illinois, plus West Virginia and Virginia and all states northeast of that with scattered populations in the southern Appalachians
USDA Growing Zones: 3 – 6
Average Size at Maturity: 10 – 30 ft tall, 10 – 15 ft spread
17. Western Mountain Ash (Sorbus sitchensis)
Western Mountain Ash is a pretty single to multi-stemmed shrub that spreads almost as wide as it does tall.
In spring, it has lovely white flowers followed by clusters of red or reddish berry-like pome fruits that stay on the tree and feed the birds throughout the cold winter months.
It is easy to grow in sun or light shade in any soil type, from sandy to clay, mildly acidic to mildly alkaline, rich or poor, but it prefers it to be moist and well-drained.
It can tolerate strong winds but does not do well with direct exposure to salt spray from the ocean.
Also, not being a true ash, this North American native has no susceptibility to the Emerald Ash Borer.
Identifying Features of the Western Mountain Ash
Western Mountain Ash is a medium to large-sized shrub with 1 – 8 trunks and reddish-purple bark that matures to grayish-red.
Winter buds are reddish, dull, not viscous, and sparsely or densely rufous-villous.
Leaves are odd-pinnate with persistent stipules and 7 – 13 opposite or sub-opposite leaflets that become mostly hairless.
Leaflets are 0.7 – 2.4” long, 2 – 3 times longer than wide, oblong to narrowly elliptic, oblanceolate, ovate, or obovate, dull to shiny green, and slightly glaucous blue-green below. Margins are entire to coarsely serrated, sometimes doubly serrated, and tips are obtuse or acute.
Flowers are in 12 – 80-flowered rounded 0.8 – 3.15” panicles.
Flowers are ½” across with five white or rarely pinkish-white rhombic to ovate petals, 15 – 20 stamens, and 3 – 5 styles.
Fruits are berry-like pomes that are pinkish-red, red, or purplish, dull, glaucous, rounded to broadly elliptic or obovoid, and up to ½” wide.
Often Confused With: Western Mountain Ash is mostly confused with European Mountain Ash which has 9 – 15 serrated flat medium-green leaflets with villous hairs on its lower surfaces and on its bud scales, smaller flowers with rounded petals, and slightly smaller orange-red fruits. Sometimes it is confused with Greene’s Mountain Ash (Sorbus scopulina), but that one has 9 – 15 shiny dark green leaflets, inflorescences with up to 200 flowers, and shiny red fruits that are not glaucous.
Other Common Names: Sitka Mountain Ash, Pacific Mountain Ash
Native Area: Western North America from southern Alaska south through British Columbia, Canada to California, and east to Idaho and Montana in the USA
USDA Growing Zones: 5 – 8
Average Size at Maturity: 3 – 15 (to 20 ft) ft tall, 3 – 10 ft spread
18. European Mountain Ash (Sorbus aucuparia)
European Mountain Ash is a full sun lover, easily grown in acidic, moist, well-drained soils.
It prefers areas with mild summers and cold winters and grows well in mountainous areas.
It will not tolerate very hot summers and can be prone to various diseases or insect pests.
It produces attractive white flowers followed by attractive orange-red berry-like fruits that are loved by birds who feed on them throughout the winter.
It has been introduced in numerous states and provinces throughout North America and is considered invasive in several of those. If you live in North America, try growing one of our many gorgeous native mountain ashes instead.
Identifying Features of the European Mountain Ash
European Mountain Ash is a small tree with a narrow upright-oval crown that becomes more rounded and open as it matures.
It has odd-pinnate compound leaves with 9 – 15 serrated flat medium-green oblong to somewhat lanceolate leaflets, each about 2.5” long with acute to obtuse tips. They turn yellow to reddish-purple in the fall.
It has long villous hairs on its twigs, bud scales, and underside of its leaves.
Small, white bisexual flowers about ⅓” across have five white rounded clawed petals and stamens that are about the same length as the petals. Flowers appear in flattened corymbs in May.
Fruits appear in late summer in pendant clusters of orange-red berry-like pomes up to 0.4” across.
Cultivars are available with pink, yellow, or bright red fruits.
Often Confused With: European Mountain Ash is often confused with American Mountain Ash, but that one has 11 – 17 dull green to yellowish-green lanceolate to oblong-lanceolate leaflets with tips that are acuminate to long-acuminate rather than acute to obtuse.
Other Common Names: Rowan, Mountain Ash
Native Area: Europe through western Asia to Siberia
USDA Growing Zones: 3 – 6
Average Size at Maturity: 20 – 40 ft tall, 8 – 20 ft spread
Growing Ash Trees in Your Garden
Ash trees of all kinds have lovely green compound leaves and attractive fruits, making them an excellent addition to any garden or landscape.
As with any tree, it is important to do some research to ensure successful establishment in your yard.
First, be sure to understand the USDA Planting Zones and choose a tree adapted to your climate.
Next, compare your chosen tree’s soil, light, and moisture requirements to your site. Check out How to Pick A Tree For Your Yard for more information on choosing the right tree for the right spot.
Most ash trees, particularly mountain ash, are adapted to cooler climates with milder summers. But true ashes native to southern North America or southern Europe and Asia can easily handle hot, dry summers.
Young ash trees should be watered regularly to keep the soil moist as their roots become established. Mature trees usually only need watering during prolonged drought and/or very high temperatures.
Some ash trees will grow well in wet soils and even swamps, while others are more suited to well-drained or dry soils. Be sure to choose the right species for your spot.
Most ash trees tend to require full sun, but a few species will tolerate partial shade and rarely full shade.
Many ash trees are not picky about the soil type, growing in sand to clay, acid to alkaline, and rich to poor. However, some prefer richer soils or will not tolerate alkaline soils, so check your chosen species.
Most ash trees have strong and wide root systems. If planting multiple ash trees, be sure to plant them at least 60 feet apart to allow room for their roots to develop. Do not plant them too close to foundations or other structures.
Whenever possible, choose a species native to your area to enhance biodiversity and wildlife values. This is especially important but also difficult with the spread of the Emerald Ash Borer. Try to choose more resistant trees, particularly new native cultivars that are being bred for resistance.
Mountain Ash Trees are not a food source for the Emerald Ash Borer and will not become infected even in areas devastated by the pest.
Mountain Ash, being related to apple trees, tends to get diseases that infect apples. These include apple scab, fire blight, black rot, and rust.
As always, be careful with non-native species that are known to be invasive
The Emerald Ash Borer and Other Pests
Until the Emerald Ash Borer became a problem, true ash trees were mostly healthy trees. They occasionally had problems with ash bark beetles, aphids, scales, ash anthracnose, verticillium wilt, and ash dieback (Hymenoscyphus fraxineus).
The Emerald Ash Borer is an Asian beetle that has devastated ash trees worldwide, particularly in North America, where most trees show little to no resilience to this pest.
The Emerald Ash Borer is a ½” long flying beetle with a pretty metallic emerald-green exoskeleton that shimmers in the sunlight.
In North America it was discovered in the northeastern USA in 2002. Since its introduction, it has put several native North American ash trees on the endangered species lists. As it spreads west and south, it threatens more native ash species.
Signs of Infestation
The adult beetles fly to find a mate and then lay eggs in the bark of ash trees. The larval stage of the insect’s life cycle destroys the ash trees. When the eggs hatch, these larvae feed just under the bark in the tree’s living tissue, boring through it and leaving characteristic S-shaped feeding trails. As these trails coalesce, it cuts off the tree’s ability to transport nutrients to other parts of the tree, and it begins to die.
Once that happens, the leaves begin to yellow, thin, or wilt, particularly in the upper ⅓ of the canopy.
Woodpeckers come and start feeding on the trees, eating the pests. D-shaped beetle exit holes about ⅛” wide will be visible in the bark, as shown in the photo below.
Sometimes the tree starts sprouting shoots from the trunk or roots with often larger-than-normal leaves, presumably in an attempt to continue growing and photosynthesizing while the top part of the tree is dying.
If you peel back the bark on a dying tree, you will see the S-shaped feeding trails. As the infestation spreads, the bark often splits vertically and falls off the tree.
When the Emerald Ash Borer infects a region, sometimes people destroy the healthy and infected trees alike in an attempt to slow the spread. However, destroying healthy trees is unnecessary, and you may be destroying resistant genetics that could save the species.
Furthermore, sometimes the trees can be saved. It is probably futile if more than 50% of the canopy is dead or dying. But, if you catch the infestation early enough, it can be treated with insecticides.
Insecticides generally need to be applied yearly, and application methods and insecticides vary, as do which insecticides are approved for use in certain regions/counties/states, etc. Be sure to consult local professionals to find the best approved treatment in your area.
Destroying dead trees is important. Even if you cannot see the larvae, there may be eggs in the trees, so infected trees beyond saving should be burned if possible. Otherwise, the tree can be chipped and solarized in black garbage bags or under a black tarp before being disposed of in a landfill.
If the infestation is new in your area, please inform local invasive species groups or local governments of the problem so that others can be made aware. If the infestation is already known in your area, these same groups can be great sources of information on available local treatment and disposal options.
Amazing Ash Trees
Vikings believed that Odin created the first man on earth using the ash tree.
Ash tree pollen of the Fraxinus genus is considered a severe allergen in susceptible individuals, whereas mountain ash species of the Sorbus genus are considered mild allergens.
Ash tree lifespan varies from 30 to 400 years.
True ashes are some of the tallest native deciduous trees of eastern North America.
Mountain Ash fruits are loved by birds throughout the northern hemisphere. They appear to have coevolved where studies have shown that seeds that pass through a bird’s gut have increased germination and survival rates.
The wood of true ash trees is dense, very strong, yet lightweight. This makes it highly desirable for use in sports equipment, including baseball bats, bows, hockey sticks, and oars.
The flexible hardwood of true ash is also prized for use in tools, cabinetry, flooring, and household furniture. It also responds well to steaming, allowing it to be bent for use on staircase rails and other unique features.
Swamp Ash wood is ideal for musical instruments because the resonance of the wood works well with both electric and acoustic guitar bodies.
Ash and mountain ashes are widely used as ornamentals in gardens and landscapes worldwide, though true ashes have been used less in recent decades due to the Emerald Ash Borer.
Mountain Ash pomes possess anti-inflammatory properties and are also used for colds, diarrhea, and vitamin C deficiency.
Native Americans widely used white Ash as a laxative, general tonic after childbirth, as an aphrodisiac, diuretic, appetite stimulant, and for fevers, itchy scalp, lice, and insect bites.
Ash trees provide food and a habitat for many animals in the forest. The tall trees also protect the smaller understorey trees.
The flowers of all ash trees support a wide range of pollinators.
Wild rabbits, deer, and moose browse on leaves and twigs of ash and mountain ash.
Ash trees are important habitats for insect species like longhorn beetles, lace bugs, aphids, and countless caterpillars of various native butterflies and moths.
Silver-haired bats use true ash trees for nesting.
From late summer throughout winter, numerous bird species feed on the Mountain Ash species’ berry-like pomes. Birds will also feed on the seeds of the true ashes.
Now that you know so much more about these beautiful trees, you can go out and identify the amazing ash trees around you or maybe plant one in your yard to enjoy for many years to come.
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Lyrae grew up in the forests of BC, Canada, where she got a BSc. in Environmental Sciences.
Her whole life, she has loved studying plants, from the tiniest flowers to the most massive trees.
She is currently researching native plants of North America and spends her time traveling, hiking, documenting, and writing.
When not researching, she is homeschooling her brilliant autistic son, who travels with her and benefits from a unique hands-on education about the environment around him.