Trees We Care For: Ash Trees  

Whether you’re a homeowner who’s thinking about adding some new trees to the backyard or a commercial property manager who wants to ensure an existing group of trees is pruned correctly, it’s important to familiarize yourself with some of the most common trees in Michigan. This helps ensure you select the best ones to plant and get your existing trees the kind of care they need. 

We’ll try to help you do that by sharing some key information about some very special trees — the ashes. 

Michigan’s Ash Tree Species

There are a number of wonderful things about living in the Great Lake State, including the diversity of tree species that will grow within our borders. More than 75 tree species are native to Michigan, and dozens of other exotic species are commonly planted within our state’s borders.    

And of those species, approximately seven are members of the genus Fraxinus — the true ashes. 

Native Ash Trees in Michigan

There are four ash tree species that are native to Michigan, though one is quite rare. 

• White Ash (Fraxinus americana): The largest ash species in the U.S., the white ash can reach up to 90 feet in height. Named for the pale underside of its leaves, the white ash was a popular street tree before emerald ash borer (EAB) arrived in the country, and tens of thousands were planted to replace American elms killed by Dutch elm disease. 
• Green Ash (Fraxinus pennsylvanica): The green ash doesn’t grow quite as large as the white ash, though it is capable of reaching 70 feet in some cases. The green ash is quite similar to the white ash, except that it lacks the pale leaf undersides and tends to occur in damper habitats. 
• Black Ash (Fraxinus nigra): The black ash is a bit of a wetland specialist, and it grows best in areas that are low-lying, damp, or periodically flooded. It can reach 50 feet in height, and it typically produces an open, pyramidal crown. 
• Blue Ash (Fraxinus quadrangulata): Blue ash is quite rare in Michigan, and it’s only documented as growing in a relative handful of locations. It can reach heights of approximately 50 feet, and it tolerates limestone soils better than most other ashes. The blue ash can grow in damp or wet sites, and it appears somewhat resistant to EAB. 

Exotic Ash Trees in Michigan

In addition to the ash trees that are native to Michigan, a few exotic species are commonly planted in our area. 

• European Ash (Fraxinus excelsior): Another relatively large ash that can reach or exceed 70 feet in height, the European ash has never become especially common in the U.S., though it is planted on occasion. It cannot tolerate hot, dry summer weather, and it is very susceptible to EAB. 
• Manchurian Ash (Fraxinus mandshurica): The Manchurian ash is one of the only ash trees that has resistance to EAB, likely due to the fact that its native range overlaps with that of the insect. Accordingly, these 40- to 50-foot-tall trees are being planted more commonly in Michigan. 
• Flowering Ash (Fraxinus ornus): Native to southern Europe and southwest Asia, the flowering ash is another medium-sized ash species that reaches about 50 or 60 feet in height. It’s prized for its attractive, sweet-smelling flowers, but it’s unfortunately susceptible to EAB like most other ashes.  

Trees with “Ash” in Their Name That Are NOT True Ashes

There are a few other trees that commonly grow in Michigan that have the word “ash” in their name, despite the fact that they’re not true ashes. These species all belong to other genera, are not closely related to true ashes, and have different care requirements.   

• Mountain-Ash (Sorbus spp.): Known as rowan trees in Europe, mountain-ashes have leaves that look somewhat similar to ash leaves, but they’re in an entirely different family of trees (ashes are in the olive family, while mountain-ashes are in the rose family). 
• Prickly Ash (Zanthoxylum americanum): This thorn-covered tree is native to Michigan and reaches heights of about 30 feet. Its leaves superficially resemble those of ash trees, hence its common name. 
• Ash-Leaf Maple (Acer negundo): Also called the box elder, the ash-leaf maple is a type of maple tree that reaches 70 feet in height or so. Unlike most maple trees, the ash-leaf maple produces compound leaves, which resemble ash leaves. 

How to Care for Ash Trees in Michigan: A Guide for Homeowners and Property Managers

By and large, ash trees require the same basic type of care that most other native and ornamental species do. For example, they should be:

• Planted properly. Trees should be planted in holes that are at least two to three times as wide as the root ball. Be careful not to dig the hole too deep; you want the root flare to be visible above ground once the tree is planted. 
• Watered appropriately. Always provide supplemental water for at least the first year after planting a new tree, as well as during extended droughts. Long, slow, deep, infrequent soaks are ideal and help to encourage good root development.  
• Pruned regularly. Have your trees pruned to remove dead, diseased, or decayed wood regularly (once every three to five years), as well as any time you have a specific reason to do so (improve airflow in the canopy, alter fruit or flower production, etc.). 
• Fertilized as needed. Fertilizer can be helpful for supporting trees in urban areas, given the nutrient depleted nature of soils in these areas. Just be sure to test the soil first to ensure you’re addressing the specific deficiencies present. 
• Protected from damage. One of the biggest threats to residential and commercial trees is damage caused by wildlife, mowers, string trimmers, and similar things. A good mulch ring will do wonders for preventing mower and string trimmer damage, while wraps and improvised “cages” can discourage animal activity. 
• Mulched correctly. A 2- to 4-inch-thick layer of mulch placed over a tree’s root system will help retain moisture, improve soil structure, and protect roots from temperature extremes. Try to apply mulch under the entire canopy (to the dripline), but avoid piling mulch against the trunk, as it can lead to decay. 

Additionally, ash trees should be monitored for EAB and treated as appropriate. There are a few treatments homeowners may be able to carry out in some cases, but it is generally better to enlist the help of a professional arborist. 

We’ll discuss EAB further below. 

Pruning Ash Trees in Michigan

Like most other trees, ash trees will require regular pruning to keep them safe, healthy, and looking their best. Routine pruning should be carried out once every three to five years and focus on the removal of dead, diseased, or decayed branches. Other types of pruning (crown raising, crown reduction, vista pruning, etc.) should be performed on an as-needed basis. 

While you can and should have any hazardous branches removed promptly, routine and elective pruning should always be carried out in the dormant season (winter). This will help avoid stressing the trees and reduce the chances that the fresh pruning cuts will attract boring beetles. 

No matter the purpose or timing of the pruning, it is imperative that the cuts be made with the proper tool (which should be as sharp as possible to achieve clean cuts) and placed properly — right outside the branch collar. It often takes quite a bit of experience to place pruning cuts properly, so it is wise to leave this job to the professionals. 

Common Ash Tree Problems in Michigan

There are a number of different problems that commonly afflict ash trees in Michigan, but one — emerald ash borer — is undoubtedly the most problematic. Nevertheless, we’ll share some basic information about the threats ash trees face below. 

Emerald Ash Borer

Emerald ash borers are small, bark-boring beetles that are historically native to Asia. However, they were introduced to the U.S. in 2002, when they were first discovered attacking ash trees in Detroit. They’ve currently spread to approximately 25 states, and they’ve killed millions of ash trees since first arriving in the country. 

Adult emerald ash borers will lay eggs on the bark of ash trees, and then the emerging larvae burrow through the bark, into the tree’s phloem, where they tunnel and feed. This feeding and tunneling behavior destroys the tree’s phloem and other vascular tissues, which results in the tree’s eventual death. 

A few of the most common symptoms of EAB infestation include the presence of D-shaped holes in the trunk or major branches and dieback in the tree’s canopy. You may also see new sprouts emerge from the base of the tree as it tries to survive the infestation. 

There are treatments available for EAB, but they’re best applied at the very first stages of the infestation. All ash trees native to Michigan are susceptible to attacks, though the blue ash appears to be somewhat resistant. Given the threat EAB presents, most authorities discourage the planting of new ash trees at this time. 

Ash Anthracnose

In contrast to emerald ash borer, ash anthracnose is rarely serious or fatal for otherwise healthy ash trees. A foliar disease that causes small black lesions or spots to appear on the leaves, anthracnose is a fungal pathogen that is commonly found in the soil. It tends to be most common during and after cool, wet springs, but it can occur any time an ash tree has leaves. 

Anthracnose generally doesn’t require treatment, as most cases are relatively self-limiting. The tree may shed a large number of leaves, but they’ll generally be replaced with fresh, healthy leaves the following year. However, repeated anthracnose attacks can cause a tree to decline or die. 

Root Rot

“Root rot” is a bit of a catch-all term that’s applied to a variety of specific fungal pathogens, such as Armillaria. Each type of root-rotting fungus has a slightly different lifecycle and causes a different kind of decay, so you’ll need to consult with a tree-care expert to understand your tree’s prognosis and any potential treatment options available. 

The problem with root rots is that they can often go undetected until a tree is already quite hazardous. Mushrooms and conks growing on or around the base of the tree are a common sign, but they’re not always visible or noticed. To help prevent root rots from setting in, avoid overwatering your trees or piling mulch up against the trunk. 

Ash Yellows

Ash yellows is a serious disease of ash trees, caused by a microorganism called Candidatus Phytoplasma fraxini. Essentially an unusual type of bacteria, the organism lives in the phloem of trees and is thought to be spread by leafhoppers and other insects. 

There is no cure for ash yellows, and immediate removal and disposal of the infected wood is generally recommended. It can cause drastically reduced growth, as well as the production of small leaves and “witches’ brooms” — dense clusters of small branches that emerge from a healthy branch.  

Signs Your Ash Tree May Require Removal

Unfortunately, pests, disease, poor structure, decay, and poor soil conditions can make a tree hazardous to people, pets, and property. So, it’s important for homeowners and property managers to monitor their trees regularly for signs of trouble. A few of the most noteworthy clues to watch for include:

• Cavities or Hollows: Tree hollows can be subjectively attractive and provide habitat for wildlife, but they’re usually associated with significant decay.
• Cracks in the Wood: Cracks — particularly when they occur in the trunk or major branches — are a sign that a tree is already failing and requires immediate assessment. 
• Lifting or Mounding Soil: Lifting soil near the base of a tree often indicates that the roots or soil are failing, and that the tree is likely to fall over very soon. 
• Wood-Boring Insect Holes: Wood-boring insects don’t always kill trees, but some (such as emerald ash borer) are especially problematic and necessitate an arborist’s examination. 
• Premature Fall Color or Leaf Drop: Leaves that start displaying autumn colors in the summer or fall off the tree in large numbers may indicate the presence of disease. 
• Mushrooms or Conks: Mushrooms and conks that are attached to a tree’s trunk, branches, or roots indicate that the internal decay is undoubtedly present. 
• Sudden Lean Changes: Many trees develop a gradual lean over years or decades, but trees that develop sudden leans are at great risk of failure. 

If you notice any of these signs or symptoms, be sure to contact the tree-care experts at Treemendous Tree Care immediately. These kinds of problems don’t always require a tree to be removed (pruning, pest-control treatments, and other techniques can sometimes mitigate the danger presented), but you’ll need a tree-care professional to assess the trees and identify the next steps. 

Treemendous Tree Care: Your Ash Tree Experts!

No matter what kind of ash trees are growing in your yard or commercial property, you’ll want to ensure they get the care and support they need to thrive. Ash trees may provide significant value in the form of reduced cooling costs and increased property values, but they can quickly turn into liabilities if they succumb to pests, disease, or environmental threats.  

Fortunately, it’s easy for Michiganders to get expert tree-care assistance: Simply contact Treemendous Tree Care. We’ll send one of our arboricultural experts to your property to assess your trees, outline a care regimen, and provide you with an itemized estimate. From there, you can just sit back and relax, confident that your trees are in the very best hands. 

Contact us today to get the tree service you need in Fraser, Utica, Warren, or anywhere else in Southeast Michigan! 

Sources & References

• ScienceDirect – “Potential for persistence of blue ash in the presence of emerald ash borer”
  Examines whether Emerald Ash Borer (EAB) infestation allows for survival/persistence of Blue Ash in impacted forests.
  https://www.sciencedirect.com/science/article/abs/pii/S0378112716310520
• American Phytopathological Society – “Ash yellows, a disease of Fraxinus spp. …”
  Documents the distribution and impact of the disease “ash yellows” in ash trees across North America, including host range and spread.
  https://www.apsnet.org/publications/plantdisease/backissues/Documents/1990Articles/PlantDisease74n08_604.PDF
• State of Michigan – “Invasive Species: Emerald Ash Borer”
  Provides identification, reporting guidelines, and regulatory status of EAB in Michigan.
  https://www.michigan.gov/invasives/id-report/insects/emerald-ash-borer
• US Forest Service – “Tree Atlas”
  Presents habitat suitability modelling for multiple tree species under climate change, offering context for forest-health risks.
  https://www.fs.usda.gov/nrs/atlas/tree/546
• Michigan State University Extension – (file e2942)
  Offers fact-sheet-level guidance on forest pest threats and management relevant to invasive insects in Michigan.
  https://www.canr.msu.edu/uploads/files/e2942.pdf