The Michigan Homeowners Guide to Ash Trees

Thanks to their beauty, moderately fast growth rate, and significant wildlife value, ashes – including both native and exotic varieties – have been popular Michigan trees for decades. And while some ashes are currently under threat from the emerald ash borer, others are relatively immune to this pest and remain highly prized.

But whether you’re trying to decide if ash trees are right for your residential or commercial property or you’re interested in keeping those you already have healthy, it’s important to familiarize yourself with their basic biology, environmental needs, and the common pests and pathogens they face. To help, we’ll share everything the Michigan homeowners need to know about ash trees below.

Michigan’s Native Ash Trees

Four true ash species are native to the state of Michigan – the white ash, green ash, black ash, and blue ash. Members of the olive family (Oleaceae) and the genus Fraxinus, all four of these species share several key traits, including:

• Leaves: All true ash trees have pinnately compound leaves, with each individual leaf bearing between 5 and 11 leaflets. These compound leaves are arranged in opposite fashion, meaning that they emerge from the twig in pairs, with one located on one side of the stem and the other located directly opposite it. This is a key ID characteristic, as there aren’t many other trees with oppositely arranged, pinnately compound leaves in the U.S.
• Fruit: Ash trees produce a dry, single-winged fruit called a samara. It is often described as being paddle-shaped, and it appears similar to a maple samara (“helicopter”) that has been split in half. The seeds are easily visible when viewing the fruit, and they feature a thin, flat “wing” on the other side. Various details of the samara can help you determine the exact species of ash you’re looking at.
• Growth Habit: All ash trees exhibit a rounded to oval-shaped crown, and they are all deciduous, meaning that they shed their leaves in the winter.
• Flowers: Ash tree flowers are small, inconspicuous, and often emerge before the tree’s leaves in the spring. Because they’re not especially fragrant or brightly colored, they are primarily wind pollinated.
• Bark: The bark of all young ash trees is relatively smooth, but mature specimens generally develop a thick, furrowed bark with an obvious diamond-shaped pattern.

While all four of Michigan’s native ash trees exhibit these traits, they also differ from each other in several key ways, which we’ll discuss below.

White Ash

Known to arborists as Fraxinus americana, the white ash is the largest of Michigan’s native ash trees. Mature trees often reach 60 to 80 feet in height, with a 40- to 50-foot branch spread. The white ash is generally an upland species, unlike several other ash trees, which are more comfortable in swamps and floodplains.

White ashes grow at a moderate rate, though they may put on 2.5 feet of new growth per year when provided with ideal conditions. White ashes are named for the underside of their leaves, which are quite pale in color. In the fall, white ash trees produce gorgeous foliage, ranging from deep purple to gold.

Green Ash

A lowland species, the green ash ­— known to arborists as Fraxinus pennsylvanica — is the fastest growing of Michigan’s native ashes. But because it grows so quickly, its wood is also somewhat weaker than the wood of white ash. It’s a bit smaller than the white ash, with the largest mature trees generally topping out around 70 feet with a 50-foot canopy spread.

Green ash was one of the most popular street trees in Michigan, but recently emerald ash borer has killed an estimated 99% of those that were originally planted.

Black Ash

Like the green ash, the black ash (or Fraxinus nigra, as arborists call it) is a lowland species that’s most comfortable in swamps and other poorly drained areas. Also like the green ash, the black ash serves as an important food source for tadpoles, who consume the tree’s shed leaves when they fall into the water. This is thought to be due to the relatively low tannin content of black ash leaves, which is ironically part of the reason black ash trees are susceptible to the emerald ash borer.  

The black ash grows quite a bit slower than the green ash and generally remains a bit smaller, too — mature trees rarely exceed 60 feet in height. It also requires less light than some other ashes.

Blue Ash

Though it only grows naturally in a few scattered locations within Michigan, the blue ash is occasionally planted as an ornamental. It is most common in alkaline, limestone-based soils, though it may thrive in other places with proper care. The blue ash is the smallest of all four native species, as few mature specimens exceed 50 feet in height.

The blue ash is easy to identify by noting its squarish twigs — the very characteristic that inspired the species’ scientific name, Fraxinus quadrangulata, meaning four-angled ash tree.

Exotic Ash Trees That Are Often Planted in Michigan

In addition to the four native ash tree species found in Michigan, there are two exotic ash species that are often planted within our state’s borders.

European Ash

Native to a large swath of land in Europe, stretching from France all the way to Turkey and beyond, the European ash is often planted ornamentally in the U.S. In fact, it has become naturalized in some areas. Nearly as large as the white ash, the European ash (which arborists call Fraxinus excelsior) has relatively strong wood.

The European ash is available in many cultivar forms, including a very popular “weeping” form, known as ‘Pendula.’

Manchurian Ash

Thought by some to be very closely related to the green ash, the Manchurian ash — known to arborists as Fraxinus mandshurica — is also relatively small and rarely exceeds about 50 feet in height. While it can also thrive in wet, lowland sites, Manchurian ash is more tolerant of different site conditions than the green ash, and it is exceptionally tolerant of pollution, which is part of the reason it is often planted in urban areas.

Some pest-resistant cultivars of the Manchurian ash have been developed in an effort to withstand emerald ash borers, but none are completely immune to their attacks.

Mountain Ashes: Two Other Ash Trees to Know

The six ash trees discussed above are the only ones that are commonly found within the state of Michigan (whether because they’re native or commonly planted). However, there are two other trees that have the word “ash” in their common name, so some homeowners consider them to be ash trees as well.

However, these trees are not closely related to “true” ash trees of the genus Fraxinus. They’re both in the genus Sorbus and are quite different from true ash trees in numerous ways. Nevertheless, we’ll briefly discuss them both below.

·     American Mountain Ash (Sorbus americana): Native to Michigan, these small trees reach about 30 feet in height, bear pinnately compound leaves that are arranged in opposite fashion, and produce bright orange-red fruits which attract a lot of birds. They’re typically found in cool forests and live relatively short lives.

·     European Mountain Ash (Sorbus aucuparia): Often called the rowan tree, this European native is quite similar to the American mountain ash. However, this tree grows a bit larger (some reach or exceed 40 feet), and it is also more tolerant of pollution and urban planting spaces than its American counterpart. Like the American mountain ash, the European variety produces orange to red fruits.

We include these descriptions primarily to demonstrate the difference between these trees and true ash trees. But we’ll largely exclude them from the rest of this article and focus instead on the true ash trees.

Caring for Ash Trees

Aside from one major issue that we’ve referenced briefly above (and will discuss thoroughly below), ash trees are quite hardy and tend to thrive when planted in a suitable location and provided with good supportive care. The ideal conditions for each species differ, so we’ll detail them in a species-by-species manner below:

White Ash

• Sun Exposure: Full sun
• Soil Preference: Well-drained, deep, fertile soils
• Moisture Requirements: Moderate
• Salt Tolerance: Low to moderate
• Pollution Tolerance: Moderate
• Proper pH: Slightly acidic to neutral (6.0–7.0)

Green Ash

• Sun Exposure: Full sun
• Soil Preference: Wide range, including clay and compacted soils
• Moisture Requirements: Moist to occasionally dry
• Salt Tolerance: Moderate to high
• Pollution Tolerance: High
• Proper pH: Slightly acidic to slightly alkaline (6.0–8.0)

Black Ash

• Sun Exposure: Full sun to part shade
• Soil Preference: Organic-rich, poorly drained soils
• Moisture Requirements: Wet; tolerates seasonal flooding
• Salt Tolerance: Low
• Pollution Tolerance: Low to moderate
• Proper pH: Slightly acidic (5.5–6.5)

Blue Ash

• Sun Exposure: Full sun
• Soil Preference: Calcareous, well-drained soils (limestone-based)
• Moisture Requirements: Dry to moderately moist
• Salt Tolerance: Low
• Pollution Tolerance: Low to moderate
• Proper pH: Alkaline to neutral (7.0–8.0)

European Ash

• Sun Exposure: Full sun
• Soil Preference: Fertile, loamy soils
• Moisture Requirements: Moist but well-drained
• Salt Tolerance: Low to moderate
• Pollution Tolerance: Moderate
• Proper pH: Slightly acidic to neutral (6.0–7.0)

Manchurian Ash

• Sun Exposure: Full sun
• Soil Preference: Moist, fertile soils
• Moisture Requirements: Moderate to wet
• Salt Tolerance: Moderate
• Pollution Tolerance: Moderate
• Proper pH: Slightly acidic to neutral (6.0–7.0)

Emerald Ash Borer: The Biggest Threat to Ash Trees

You can’t discuss ash trees without discussing the emerald ash borer, an invasive insect that threatens most ash trees. In fact, these insects are the most significant threat to ash trees, and they’ve been responsible for killing countless millions of ash trees across the country.

We’ll explain the key facts about these insects and the threat they represent below.

History of the Emerald Ash Borer

Throughout the latter half of the 20th century, ash trees were one of the most widely planted trees by homeowners, developers, and city planners.

Given everything we’ve discussed about these trees so far, that’s easy to understand. After all, ash trees are beautiful, hardy, and tolerant of a wide variety of growing conditions. Some, like the green ash, grow very quickly, and others, such as the white ash, produce jaw-dropping fall color. They also play important roles in local ecosystems, providing yet another reason to appreciate these trees.

So, when Dutch elm disease wiped out most of the country’s American elm trees (Ulmus americana), ash trees were viewed as the perfect replacement. Unfortunately, that would turn out to be a mistake.

In 2002, the emerald ash borer was discovered in America. In fact, it was first documented right here in Michigan. Though to have arrived from its Asian homeland via packing and shipping materials, the insect found life very easy here in the U.S., where it had no natural predators and an abundance of food; unlike many of the ash trees in its homeland, which are somewhat resistant to their attacks, North American ash trees were completely unprotected.

So, the bug began feeding on our native ash trees, and it spread remarkably quickly. As of 2024, it had been documented in more than 35 U.S. states, and it’s likely already present (yet undocumented) in many more.

How Do Emerald Ash Borers Harm Ash Trees?

Adult emerald ash beetles deposit their eggs in the bark crevices of ash tree branches and trunks. A short while later, the eggs hatch, and the larvae quickly tunnel under the bark.

The larvae then begin to feed on the tree’s cambium (an important cell layer beneath the bark that produces new wood and vascular tissue), creating S-shaped galleries in the process. This effectively prevents the tree from moving nutrients from the leaves through the branches and to the roots via the tree’s phloem layer, and it also prevents the tree from drawing water up through the roots and xylem (wood) tissue.

This can all happen relatively quickly, and even the healthiest ash trees often die within two to four years of the initial infestation.

What Are the Signs of Emerald Ash Borer Infestation?

The first thing you’ll likely notice in a tree infected with emerald ash borer is a gradual dieback of the canopy branches. The leaves at the canopy’s periphery will begin to die and fall prematurely. The tree will also produce a lot of epicormic growth (water sprouts), which is the tree’s desperate attempt at replacing the lost foliage so it can survive.   

A few weeks later, you may start noticing the bark splitting. Often, S-shaped galleries will be visible upon close inspection, and you may also note D-shaped exit holes, created when the mature emerald ash borer beetles have finished pupating and begin to exit the tree.

Can You Treat an Emerald Ash Borer Infestation?

In some cases, emerald ash borer infestations can be treated with insecticides. Some of these insecticides are administered via trunk injections, while others are applied as a soil drench or trunk spray. However, in both cases, treatment is most effective for trees that have relatively new infections. Trees that have lost more than about 30% of their canopy or are already stressed by other factors are unlikely to fully recover.

These treatments can also be used preventively. In fact, that’s the recommended approach for high-value ash trees, as prevention tends to be much more effective than treatment (and help avoid the need for costly crane-assisted removals). In all cases, the treatment must be administered every one to three years to keep the tree protected from these insects.

Other Pests and Diseases of Ash Trees

Aside from their susceptibility to emerald ash borer, ash trees are relatively resistant to pests and disease. This is part of the reason that they were planted so widely as street trees. However, they can experience a few other problems, including:

• Ash Leaf Curl Aphid: Caused by tiny aphids that cause the tree’s leaves to curl or turn yellow, this problem is mostly cosmetic in nature. Trees will often recover the following season, though repeated attacks can weaken trees and lead to their eventual decline.
• Oystershell Scale: These small insects suck the sap from the tree’s twigs, branches, and bark. While minor infestations are usually not especially harmful, serious infestations can lead to dieback or death.
• Anthracnose: A fungal disease that’s most common following cool, wet springs, anthracnose causes irregular leaf blotches, early leaf drop, and distorted leaves.
• Verticillium Wilt: A soil-borne fungal pathogen that infects a tree by penetrating the roots, before moving up the stem and causing vascular problems for the tree. Verticillium wilt can lead to crown dieback, wilting, leaf scorch, and the eventual death of the tree in some cases.
• Ash Rust: This is another fungal disease that affects ash trees. It’s typically only a cosmetic issue that causes bright orange or red spots to appear on the leaves.

Michigan Ash Trees: FAQ

Still have questions about your ash trees? We’ve rounded up some of the most common ash-tree questions below and answered them for you!

What are the disadvantages of an ash tree?

Ash trees provide a number of benefits, and they have relatively few downsides. However, they do present one problem – susceptibility to emerald ash borer – which is quite serious. Virtually all North American ash trees will eventually die from this pest without treatment, which represents a pretty significant disadvantage when compared to other species that don’t suffer from as many pest problems.

Why shouldn’t you plant ash trees?

The biggest reason many arborists discourage homeowners from planting ash trees is the emerald ash borer — an invasive insect that kills most ash trees within a matter of years. Nevertheless, you still can plant ash trees (provided that it is legal to do so in your area) if you’re willing to treat them.

Should I get rid of an ash tree?

All three removal decisions should be made on a case-by-case basis after consulting with a professional arborist. However, ash trees that are either dead or seriously infected and located near high-traffic areas or homes should typically be removed to reduce the risk they present. Just be sure to contact an arborist if you notice signs like crown dieback or the tree’s leaves turning brown.

Are ash trees worth saving?

This is a subjective decision, but in many cases, ash trees can provide significant value, which outweighs the cost of ongoing treatment to protect them from emerald ash borers. Nevertheless, this is a decision every homeowner should make for himself or herself, in consultation with a professional arborist.

What is the lifespan of an ash tree?

Ash trees aren’t especially long-lived trees. While there are individual ash trees that have been documented living for a few hundred years, most only live for about 75 years or so.

How tall do ash trees get?

The largest ash trees may approach 80 feet in height, with occasional specimens surpassing this.

Should you remove dead ash trees?

Dead trees that are located near structures or high-traffic areas should usually be removed. However, if they’re located in isolated areas, they can often be retained to provide wildlife habitat.

Should I have dead ash tree branches removed?

It is usually wise to have dead tree branches removed, regardless of the species in question. Dead branches represent a safety hazard, as they may fall on humans, homes, or hardscapes below. Dead branches may also signify the presence of EAB, so it is wise to contact an arborist promptly whenever you see dead ash tree branches.

Get the Care Your Ash Trees Need!

Whether your ash trees are thriving and you’d like to get them the support they require, or they’ve already succumbed to emerald ash borer and require removal, you want to work with a tree company you can trust. Longtree Tree Service has been providing Michigan homeowners with top-notch tree-care services since 2019 and building a reputation as the area’s most trusted arborists. We’d love to help with all of your tree-related needs.

Contact us today and request your free consultation!

References

• Michigan State University Extension. Ash Tree Identification (E2942).
  https://www.canr.msu.edu/resources/ash_tree_identification_e2942
• Holden Forests & Gardens. Fraxinus spp. (Ash) Nature Profile.
  https://holdenfg.org/nature-profiles/fraxinus-spp-ash/
• Michigan Department of Natural Resources. Emerald Ash Borer – Invasive Species.
  https://www.michigan.gov/invasives/id-report/insects/emerald-ash-borer