T. Davis Sydnor
One thing that seems to be human nature is for people to search for the one plant that will serve all functions and sites equally well. Of course that tree or shrub does not exist. Sites can vary such that a plant could be a good choice for a specific location and would be a poor choice for a site a few feet away. All plants have good and bad features. The key to reducing maintenance costs is to match the plant to the site as closely as possible to minimize the undesirable characteristics. No plant is so bad that it cannot be used to good advantage nor so good that it cannot be a poor choice.
In marketing trees, the tendency is to concentrate on the characteristics such as flower color, fall color, variegation patterns, and other highly marketable characteristics. Undesirable characteristics are often ignored or minimized to close the sale. Patent laws in the United States compound the problem. Growers cannot afford to test the tree to ensure that it has a 25-year service life if the patent lasts for 17 years. Desirable plant lists can cause problems by making unstated assumptions. All planting sites are assumed to be normal. Serious plant selection errors can be made although the intent was good.
A list of trees commonly grown in Ohio appears here. Undesirable and less well-known desirable characteristics of these commonly grown trees will be the focus of this report. Knowing these potential faults will enable landscape designing, contracting, and maintenance personnel to make better choices and to plan realistic maintenance. This report is not an attempt to sway people from using popular plants but an attempt to give more complete information on popular plant material to maintain a firm's profitability. The trees covered are listed alphabetically by scientific name in Table 1 and in the body of the text. Table 1 will enable you to find the write-up you need more easily.
| Table 1. An alphabetical listing of the scientific names of trees covered in this article. The paragraph number in which the tree is covered is given. | ||
|---|---|---|
| Scientific Name | Common Name | Paragraph |
| Acer X Freemanii | Freeman Maple | 1 |
| Acer rubrum | Red or Swamp Maple | 2 |
| Acer saccharum | Sugar / Rock Maple | 3 |
| Amelanchier x grandiflora | Apple Serviceberry | 4 |
| Betula nigra | River Birch | 5 |
| Carpinus betulus | European Hornbeam | 6 |
| Fraxinus americana | White Ash | 7 |
| Fraxinus pennsylvanica | Green Ash | 8 |
| Gleditsia triacanthos | Thornless Honeylocust | 9 |
| Malus species | Crabapples | 10 |
| Platanus X acerifolia | London Planetree | 11 |
| Pyrus calleryana | Callery Pear | 12 |
| Quercus palustris | Pin Oak | 13 |
| Tilia cordata | Little-Leaf Linden | 14 |
Height to 80 ft.
The major drawback for this plant is its close relationship to silver maple, the most over-planted maple in Ohio. This is a red by silver maple cross and as such has inherited much of the urban tolerance of the silver maple. One must also assume that some structural instability of silver maple has been inherited as well. These trees may need to be pruned to guarantee that they have a structurally stable branching pattern.
'Autumn Blaze' has the best fall color, but 'Celebration' has the better branching pattern. 'Armstrong' maple has an upright habit for the first 20 years and has a proven record of survival under urban conditions. 'Armstrong' has been sold for years as a red maple in the nursery trade but is now acknowledged as a Freeman maple.
Silver maple is the longest-lived maple in Ohio's urban areas. The life expectancy of Freeman maple is expected to be greater than 30 years. Freeman maples appear to tolerate wind and alkaline soils. These trees are also more tolerant of wounding than red maple. Like silver maple, this plant is likely to live long enough to outgrow a small site if it is improperly sited.
Under no circumstances should this large tree be used in a tree lawn less than six feet wide nor should it be used under power lines. Freeman maple's fruiting characteristics are variable but can be a nuisance in some years.
Height 50-60 ft.
The bark is thin, and the wound response is poor. The tree must be protected from physical damage and should not be used in damage-prone areas such as tree lawns. It requires acid soil and is less tolerant of neutral soils than most other maples and even pin oak. Growth rates are slow in urban situations. Life expectancy in an urban situation is 20 years or less with trees dying before reaching eight inches in caliper.
Red maple's moderate size allows it to be used as a shade tree in suburban areas with acid soils. This plant has a rounded and regular outline with a 1.5 to 1 height to width ratio. The plant can adapt to low-oxygen situations if given time to adapt. Remember most nursery trees are grown in well-drained situations. Red maple is dioecious. Male plants can be selected if fruit is not wanted. Maturing fruit is red turning tan when mature in mid-June and can be ornamental.
The attractive fall color and grey bark are the principal reasons that this plant has been so popular during the last 30 years. 'Red Sunset' (a female) and 'Autumn Flame' (a male) are the best commonly grown cultivars for Ohio. 'Red Sunset' has red fall color and 'Autumn Flame' has yellow to orange fall color.
Height 50-80 ft.
The sugar maple is intolerant of urban sites. This is the principal climax forest tree in much of Ohio. It is beautifully adapted to a forest environment and is shade tolerant when young. New subdivision environments are not climax forests but are similar to an open field. Open fields are disturbed sites that are colonized first by weeds and pioneer tree species. Sugar maple does not adapt well to the increased light, heightened drought, and competition from grass found in suburban areas. Service lives are less than 10 years in an urban site, 25 years in a suburban lawn, and more than 40 years in a woodland setting.
Sugar maples, as do most maples, requires structural pruning to produce a stable branching pattern. Co-dominant leaders are normal when open grown. Shade imposes a more desirable branching pattern. Storm tolerance appears similar to other maples.
The wound response of sugar maple is excellent. A strong wound response allows late winter to be the time to tap sugar maples and to collect the sap for maple syrup. Wood density is higher than red and silver maples. The lumber trade calls this tree hard maple due to its density.
Many named cultivars are available in the nursery trade. 'Green Mountain' is the most popular cultivar but does not appear to differ from the species in stress tolerance as reported. 'Green Column' has not been evaluated long enough to be sure but may be more stress tolerant than the species.
Height 25-35 feet
Forestry literature suggests that this is a pestiferous tree while horticultural literature advances serviceberry's pest resistance. The resolution to the contradiction is that it takes years for a newly introduced tree to be planted commonly enough to support a pest population. Problems have been building for five or more years. Serviceberry is a host to a variety of insects and diseases. The most serious is the lacebug that can turn the foliage white. Pear slugs, aphids, borers, and spider mites can also exact a toll. All insect and disease problems have been cosmetic.
Twenty years is the service life of this native tree in an urban environment despite the cosmetic insect and disease problems. This tree will tolerate restricted root areas better than most trees. The biggest problem in urban areas is the thin bark that provides little protection from mechanical damage. Although mechanical damage is the most limiting factor in urban situations, this may not be a concern in a residential setting.
This tree can be grown single or multi-stemmed. Serviceberry is a forest understory tree and can tolerate shade. Given time, the tree can adapt to poor drainage. The flowers are borne early but are frost tolerant, while magnolia is frost sensitive. Fruit can be eaten. If you want a tree that produces fruit, you can substitute serviceberries for blueberries in recipes. This assumes that you beat the birds to the fruit.
Height 50-60 feet
This birch is generally southern in distribution and tolerant of the heat and high soil temperatures found in the South. Southern Ohio is the northern limit of this tree's natural range. River birch is subject to several cosmetic insect and insect-like pests. The spiny witch-hazel gall aphid can cause some defoliation in some years. The problem is more severe when birch and witch-hazel are grown in close proximity. Birch leaf miner is generally a cosmetic problem for river birch.
The most serious problem is its alkaline soil intolerance. Iron chlorosis is the factor determining life expectancy. In acid soils river birch will last more than 25 years, but in alkaline soils around 15 years is to be expected. Since concrete, mortar, and limestone all increase the soil pH, river birch does poorly in some urban areas.
Bark color ranges from cinnamon to ivory. Some people are surprised when the tree produces mature bark that looks similar to a white oak. Only trees that are two to 10 inches in diameter have the exfoliating bark. The named selection 'Heritage' was selected for light colored bark. 'Heritage' was originally sold as a white birch substitute due to the light exfoliating bark and resistance to the borer that kills the white-barked birches. 'Heritage' grows more slowly and more irregularly than the species and thus is less desirable.
Foliage is a deep green in the summer. Lower branches sweep downward, allowing this plant to remain foliated to the ground. Fall color is poor. This tree grows rapidly and can reach a large size. This tree is often grown with multiple stems. In most situations only one or two stems will reach maturity. Turf does well in the dappled shade of river birch. Many other trees such as oaks, maples, and beeches shade out and kill turf.
Height to 30 feet
This tree is of European origin as the name suggests. The performance of the American hornbeam might best explain its cousin's performance. American hornbeam is a forest understory tree that is pruned to the ground every 15 years or so by the hornbeam borer. Borers attack stressed or overmature trees. High light, drought, and transplant shock are all stresses that can result in a borer attack. Multiple suckers arise to replace the dead top in time.
The most popular selection of this tree is the upright European hornbeam. This tree has a habit that is three times higher than broad. The canopy is regular, and the foliage is dense, resulting in an attractive young tree. Habit changes rapidly for those trees living longer than 20 years. By 40 years of age, the tree, including the upright cultivar, will be twice as broad as tall. Avoid the tendency to try to use this tree in a restricted space because of its narrow, juvenile growth pattern. Such restricted spaces are often stressful and increase the likelihood of a hornbeam borer attack.
Transplanting is more difficult than average. Spring transplanting is preferred. The life expectancy is 20 years in an unstressful site but only eight to 10 years in an open, tree lawn site. Hornbeam borer seemingly attacks without warning. In truth, loss of foliage density and welting of the bark are present, but often go with out detection by the homeowner.
Height to 75 feet
White ash is the most common native ash to the state of Ohio. It exists as a secondary invader species in nature and does well in moist, well-drained sites. It does poorly in urban sites although it transplants well into such sites. Parks and open areas are ideal sites for this tree. This large plant is inappropriate for planting beneath power lines or in small tree lawns.
Tolerance to poor drainage, restricted root space, and drought is poorer for white than for green ash. White ash is more tolerant of lilac and ash borers than is green ash. Life expectancy in a tree-lawn situation would be around 15 years. It would be increased to 30 years in a lawn environment if irrigated during drought periods.
Fall color ranges from yellow to purple with brown as an intermediate color. Several named cultivars have been selected for wine fall color. 'Autumn Applause' and 'Autumn Purple' are the most popular. No differences have been observed in sensitivity to insects or disease among the cultivars.
Stress intolerance is usually seen as drought sensitivity. Numerous cankers are followed by twig dieback and death over a period of several years. Ash yellows is caused by a mycoplasma-like organism (MLO) and may be associated with declining trees. Ash yellows has been a serious threat to white ash in northern Ohio.
Height to 50 feet
Green ash is native in Ohio but its range extends further west than white ash. Green ash is more stress tolerant than white ash. The growth pattern is more irregular than white ash. Both white and green ash are fast growing when small. Green ash does not get as large as the white ash, but the smaller size may be desirable in urban situations. Green ash can tolerate restricted root spaces such as sidewalk cuts.
Lilac and ash borers can be serious problems for recently transplanted trees. A spray program is desirable for one or two years to get the green ash established. Once established the spray program can usually be eliminated unless there are many infested trees nearby. Green ash should be used sparingly to prevent a build up of the borers. Life expectancy of green ash is usually determined by the borers. Fifteen years can be expected in tree pits while 30 years is common in lawn situations where borer populations are low to moderate.
Named cultivars have been selected for a variety of characteristics including cold hardiness ('Patmore'), habit ('Summit'), and foliage color ('Urbanite'). 'Summit,' with its more uniform habit, is the most popular. Most of the named selections of green ash are male and fruitless. Differences in sensitivity to insects or disease have not been observed among the cultivars. Ash yellows is reportedly less of a concern for green ash than for white ash. Ash yellows has been seen more often in northern Ohio.
Height to 75 feet
This tree is uncommonly found in the wild but has been heavily planted for the last 30 years in urban areas in the Midwest. The rapid growth for the first 10 years and the lacy foliage have been major assets for many designers. The light shade cast by honey-locust allows for good turf growth beneath the crown of the tree.
Honeylocust's habit is highly variable. Some cultivars may be too irregular to suit some people's desires. Early reports suggested that the cultivars were fruitless but this has not been true for any cultivar. Cultivars generally fruit less heavily than the species but all cultivars have fruited. 'Halka' fruits more heavily than most cultivars.
Earlier honeylocust was listed as stress tolerant. This is not so since stress results in sensitivity to honeylocust borer. Honeylocust borer causes the plant to die seemingly without warning. A lawn environment is as much stress as can be tolerated over time. A preventive spray program may be needed to get this plant established where a honeylocust borer population is active.
In the 1960s this tree was touted as insect and disease free. Today this tree is a good example of the caution that you must have a host (tree) population to support a pest population. This tree is present in sufficient numbers to support a variety of insect and disease problems. The tree is not cold hardy past -25 degrees F. Fortunately, most problems are cosmetic, but Thyronectria canker and honeylocust borers are potentially fatal.
'Skyline' has been the most consistent cultivar. 'Sunburst' (aurea) has the best record of the yellow-foliaged selections. Despite the problems, this plant will still give a life expectancy of 30 years in a lawn environment. 10. Malus species - Crabapples Height 25-50 feet
There are many named crabapples that are available in the trade. Flower colors range from white to pink and red. Summer foliage colors vary from green to wine. Fruit color ranges from green to yellow to orange and red. Flower, foliage, and fruit colors are often the reason for selecting a specific cultivar. One should use cultivars that are disease resistant, first, and then select for ornamental characteristics. Apple scab and particularly fireblight resistance are important in selection of these plants. Crabapples are the longest-lived flowering trees used in Ohio with life expectancies of 30 to 40 years for fireblight resistant selections.
One cultivar of note is 'Spring Snow,' an essentially fruitless cultivar. Crabapples begin to spread as the plants age. A crab-apple with an upright habit when it is small will become more wide spreading with age.
Crabapples are tolerant of restricted soil space and will tolerant alkaline soils. These plants handle storm loading very well. Structural pruning is needed for most selections. Wound response has been excellent. These plants can be grown under power lines and other restricted spaces quite nicely. This has been a very satisfactory tree in the urban scene. Suckering is a problem for all cultivars. Using specific rootstocks and own root production are being evaluated for reducing this problem.
Height to 75 feet
This tree is an interspecific hybrid between the American sycamore and the Oriental planetree. The oriental parent is smaller than sycamore, but the resulting cross is large by any standard. A large tree is inappropriate in restricted root spaces and beneath power lines. Foliage is bold with a disappointing fall color. The exfoliating bark is showy but less so than American sycamore. Transplant success is high even into stressful sites.
'Bloodgood London' planetree is the most popular cultivar but it is not reliably cold hardy in Ohio. 'Bloodgood' is more sensitive to cankerstain than the species. Anthracnose resistance is used to market 'Bloodgood' but what does it mean? While anthracnose causes defoliation, it does not cause death as does cankerstain. Remember that Bloodgood is properly listed as disease resistant (an-thracnose) although it is sensitive to a fatal disease. The National Arboretum recently released two new cultivars but they are reported as less cold hardy than 'Blood-good.'
Originally this plant was thought to be stress tolerant. Time has shown this to be false. The Oriental planetree is only hardy to 0 degrees F. The resulting cross is much less hardy than American sycamore.
Cankerstain is a disease aggravated by cold temperatures and high stress. Cankerstain has destroyed many plantings from New York to Ohio and beyond. Temperatures below -15 degrees F can result in outright kill. A service life of eight to 10 years can be expected in tree lawns and similarly stressful sites due to cankerstain.
Height 40 feet
Callery pear has performed well in urban situations for 30 years. The size is ideal with mature heights high enough to allow vehicular and pedestrian access beneath the canopy. The major problem has been the tendency of Callery pear to break up in storms as the plant exceeds eight inches in caliper. Formation of many co-dominant leaders results in structural instability. Wood is brittle. Structural instability must be addressed early with corrective pruning. If this is done, we can enjoy the urban tolerance of this plant without the increased risk of failure.
Wildlife is attracted both by the fruit and for nesting. The very dense branching patterns encourage nesting by birds. Several cities have found that nesting can be a problem in urban sites due to the bird droppings. Pruning to stabilize the branching pattern might also reduce nesting since an open branching pattern discourages nesting.
Selections can be chosen that have more storm-resistant branching patterns. Cultivars with potentially better branching patterns include 'Aristocrat,' 'Autumn Blaze,' 'Chanticleer,' 'Cleveland Pride,' 'Gladiator,' 'Metropolitan,' and 'Valiant.' Increased disease sensitivity and increased fruit size may be present in these newer cultivars. Experience to date with 'Brad-ford' can be beneficial as it is risky to assume that everything to be learned about the newer cultivars will be positive. Remember, the 30 years of experience with 'Bradford' is lacking in the cultivars listed earlier.
Pin oak has been something of a hate object for 25 years. The reason for concern is that the tree is intolerant of high pH soils. This is a partial truth. In Ohio, as you go from the southeast to the northwest across the 3-C line (a line defined by Cincinnati, Columbus, and Cleveland), you go from red maple to pin oak dominating the wetland woods. So we see that pin oak dominates wetland woods in the alkaline soil regions of Ohio. Native pin oak is more tolerant of neutral to slightly alkaline soils than red maple.
Why do many pin oaks exhibit iron chlorosis? In the 1940s and 50s the nursery industry in the United States began to diversify. A seedling nursery industry developed in the McMinnville, Tennessee, area and provided seedlings for much of the United States. Pin oak is native there and served as the seed source for pin oaks produced in the United States. Tennessee pin oak was falsely assumed to be the same as Ohio pin oak. Pin oak in the McMinnville area has adapted over the millennia to a soil pH of 4.5 to 5.5. Is there any wonder that McMinnville pin oaks develop an alkaline soil intolerance when grown in soil 100 to 1,000 times more alkaline than the soil in which their parents grew?
The trees in the McMinnville area can be called a seed source, provenance, or ecotype and vary from other seed sources within the plant's native range. These differences may be as important to landscape function in Ohio as the neutral to slightly alkaline soil tolerance of Ohio pin oaks is. Several Ohio nurseries are now offering pin oak from locally adapted seed sources. In Ohio, nurseries should ask for and use locally adapted seed sources to enjoy the landscape advantages of pin oak while protecting the customer.
If you are dealing with a chlorotic pin oak, the first step should be to plant an adapted replacement tree. The second step should be to try to lower the soil pH to 6.0 in the area with sulphur. Ohio's heavily buffered soils may require 10 years or more to lower the pH, so you will not see any rapid changes. Iron treatments such as trunk injection change the foliage color but do not return the tree to health or extend the tree's service life. Chlorotic trees usually decline and die over a 20-year period if the pH cannot be raised. Micronutrient deficiencies frustrate homeowners and maintenance personnel as well. Spending large amounts of money in a futile attempt to correct a micronutrient problem may cause you to lose a good customer.
Pin oaks are the most easily transplanted trees in the red oak group. Pin oak is more tolerant of soil compaction, construction activity, and wet soils than other red oaks. Tolerance of large tree lawns has been better for pin oak than other red oaks where adapted seed sources have been used. Response to wounding and structural stability of oaks is better than many other trees. Oaks are also resistant to serious insect problems except gypsy moth. Oak wilt is a local problem in most situations. Pruning near roads may be increased by pin oak's tendency to retain lower foliage although this can be an asset if screening is needed and the size can be tolerated.
Height 60 feet
This plant has done well in urban situations although it shows an interesting response to drought or restricted root space. The plant just sits in a dwarfed condition and neither grows nor dies. When in the stunted condition, the plant could be used under power lines. The tree should give a 20-year life expectancy in stressful sites and 30 years in a lawn environment.
Structural pruning will be needed to space branches, reduce the number of co- dominant leaders, and ensure long-term structural stability. Little-leaf linden has very low density wood that can lead to breakage and increase the need for structural pruning. Lindens have a weak wound response that can lead to decay. Decay is often extensive and may result in a serious defect.
Fall color is poor in most years. The uniform branching and regular outline are its major assets as a young plant. The plant becomes rounded with age. Growth rates are highly variable. Many similar cultivars are available. 'Greenspire' appears to have the best growth rate. Insects are a significant problem with gypsy moth and Japanese beetle being the most serious.
An interesting problem for all lindens is the flowers. June flowers are very fragrant; that is good, but bees are attracted in swarms. Some people are sensitive and can be killed by bee stings. People who might be sensitive to bee stings should not be seated under the low crown of any linden tree in June.