#11  Read About Trees that Tolerate City Life
                                                             Edited by Len Phillips, updated January 2023

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The intent of this Topic is to provide lists of trees that are most suitable for dealing with specific problems that urban trees might encounter.  When the arborist or landscape architect is selecting a tree for a particular site that happens to have compacted soil, for example, the arborist would select a tree listed in the compacted soils section.  Another site might frequently experience drought, very hot summers, and air pollution.  This would require looking at three different lists to select the trees that are common to all three lists.  

The final section in this topic article provides a list of trees that will tolerate five or more of the ten specific urban environment problems mentioned in this topic.  These trees are also the ones that are overused because every arborist and landscape architect knows they will do well in most urban locations.  They are the most tolerant trees that will manage to grow in difficult urban sites.

Keep in mind that the lists of trees throughout this topic are the species that might tolerate the various problems found at an urban site in the United States, but the concept can be used anywhere in the world.  

After making the final species selection, the arborist might want to consider using a cultivar of the species.  Most cultivars have been selected by nurseries and researchers not only because a tree has exceptional beauty, but because it also has improved tolerance to poor quality soil or a tree having thicker and waxier leaves and thus is able to shed pollutants and salt spray off the leaf surface in rain storms.  It might be a tree that was found thriving in a very hot region, a site with alkaline soils, or a tree that survived a drought.  Most often they are selections that have disease resistance and tolerate pest attacks.  There are also some cultivars, such as Sienna Glen Freeman Maple or Zumi Calocarpa Crabapple, that are very tolerant of urban conditions, but the species is not.  So, keep looking at the many cultivars that make very good choices for growing in the most difficult of locations, our city landscapes.

Urban and Environmental Conditions
Environmental conditions tend to be more varied in urban areas than in less developed areas.  For example, asphalt surfaces surrounding one site make it hot and dry.  Reflected light, wind, temperature, and soil conditions in the city can change abruptly from one spot to another.  Seasonal variation in urban areas may also be extreme compared to more natural areas.  A site may be hotter in the summer and colder in the winter.  Or, it may be drier in the summer and wetter in the winter due to soil compaction and the presence of paved surfaces.  However, the city as a whole generates heat that usually keeps temperatures warmer in all seasons than the temperatures in nearby natural areas.

While it is not possible to generalize about the severity of urban conditions, conditions do vary considerably, and it is wise to assess each site individually.  Be sure to consider changes that are planned in the vicinity, even if plans are not yet final.  The construction of streets and buildings, re-channeling surface water, and routing utility corridors can all affect the ability of a site to provide for the needs of trees. 

Urban conditions are frequently more severe for the growth of plants than in natural environments.  On the other hand, conditions could also be better with irrigation, better maintenance, and a lack of competition.  While it is best to anticipate urban evolution, it is safe to assume that plants and people will always have to adapt to unforeseen changes. 
                                                Trees that Tolerate Drought

Severe drought can result in trees having decreased resistance to pests and diseases, a decrease in leaf size and number, and an overall decline in growth and vigor. 

Growing Trees
The following practices should be implemented for responding to water resource challenges during reduced water availability: 
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  • Deeply soak trees and shrubs only after they show initial signs of water stress and apply the water in the morning or evening during periods of low sun and heat, (between 9 pm and 9 am) to prevent excessive evaporation.  Ideally, when the  soil reaches 60-70% of water capacity the best growth will occur (visually light brown soil color).  This is because the soil has the best balance of soil, water, and air; both environmental variables that are important for tree growth.  Trees will tolerate soil moisture down into the 35-45% range (visually 'bone dry') and, although they stop growing, they will survive and start growing again when re-watered.
  • When concerned about drought, plants can tolerate drought as long as they are not also exposed to a high vapor pressure deficit (high temperature & low relative humidity). It is the combination of no available soil water and high atmospheric evaporative demand that create conditions causing plant death due to drought.
  • Use a drip emitter, a water bag, soaker hose, targeted bubbler, or other low-flow garden hose to direct water to the tree's roots (not the trunk), and allow the water to slowly seep deep into the soil.  A slow trickle is the most effective method for absorption by tree roots.  Watering bags provide an excellent mechanism for ensuring a slow drip which infiltrates into the soil.  Watering with a hose at a high rate usually results in run-off and rapid evaporation, and encourages root growth near the surface, increasing the tree’s susceptibility to water stress.  The water bags can be removed from the base of the tree after the first season  at the new site.  However, the water bags are also very suitable for watering trees during a drought.
  • Cover bare soil with a  3” – 4” (7 – 10 cm) layer of mulch to retain more soil moisture.  Irrigation should be set so it wets the soil under the mulch, or irrigates long enough to thoroughly saturate the mulch area.
  • Autumn planted trees and shrubs have demonstrated an increased ability to survive moderate moisture levels compared to those transplanted in the spring or summer

Installing Trees  
  • Installing smaller trees of 2 in. (5 cm) caliper or under for deciduous trees and 6 feet (1.8 m) or under in  height for evergreen trees, will reduce the monetary investment and the risk of tree death during drought periods. 
  • Installing a smaller tree allows it to establish more quickly than installing a larger tree and this will require less maintenance over time.
  • Installing trees during times of drought and water restrictions should be done with caution.  An understanding of the risks and consideration of proper maintenance activities necessary to establish trees during these periods is crucial.  Also keep in mind that pines are more drought tolerant because the needles are covered with a thick waxy coating and stomates are down in deep pits in the needle where they are protected.
  • Keeping trees in the landscape helps reduce soil erosion by stabilizing soils and intercepting rainfall.  It is important to keep the limited rainfall available for tree growth instead of becoming runoff.
  • Consider installing perforated pipe running from street-side catch basins to newly planted public trees.  This provides water for the tree and reduces stormwater runoff and irrigation requirements.  A second perforated pipe just below the root ball should be connected to the storm drain to drain surplus ground water.
  • Proper mulching and adherence to watering guidelines for trees and shrubs will help establish newly installed trees in times of drought.
  • Factors to consider when installing trees and shrubs include soil conditions, available space above and below ground, exposure, moisture, and light requirements.
  • Select trees from species listed below that are hardy to the region.
 
Installing Trees During a Drought
Installing trees and shrubs during drought can be risky.  If watering restrictions are in place, establishing trees in a semi-arid region may be difficult enough without an extended drought to contend with.  However, by eliminating all tree plantings, many opportunities to sustain the urban forest will be missed.  It is critical to not only have a diversity of species in the landscape but also diversity in the age of the landscape.  This means installing  new and replacement trees each year, even during times of drought, to replace trees that are lost to drought, age, injury, and other causes.

Carefully installed replacement trees continue to maintain soil stability, reduce soil erosion, control and utilize storm water runoff, shade moisture-starved lawns and reduce energy usage by shading homes in summer and blocking winds in winter.  A well-stocked urban forest also acts as an air filter and purifier, absorbing carbon dioxide and emitting oxygen to help provide cleaner air for human consumption.

Large Drought Tolerant Trees 
Botanical Name     Common Name   
Acer leucoderme  Chalkbark maple
Acer platanoides  Norway maple
Acer pseudoplatanus Sycamore maple
Acer rubrum    Red maple
Acer x freemanii  Freeman maple
Alnus glutinosa  Common alder
Betula lenta  Sweet birch
Calocedrus decurrens  Incense cedar
Carpinus betulus  European hornbeam
Carya illinoensis  Pecan
Castanea sativa  Spanish chestnut
Catalpa speciosa  Northern catalpa
Cedrus atlantica 'Glauca'  Blue atlas cedar
Cedrus deodara  Deodar cedar
Cedrus libani  Cedar of Lebanon
Celtis laevigata  Hackberry
Celtis occidentalis  Hackberry
Cladrastis kentuckea  Yellowwood
Cryptomeria japonica  Cryptomeria
Cunninghamia lanceolata  China fir
Cupressus arizonica  Arizona cypress
Diospyros virginiana  Persimmon
Eucommia ulmoides  Hardy rubber tree
Fraxinus americana  White ash (in non-EAB infested areas)
Fraxinus pennsylvanica  Green ash (in non-EAB infested areas)
Ginkgo biloba (male)  Ginkgo
Gleditsia triacanthos  Honeylocust
Gleditsia triacanthos inermis  Thornless honeylocust
Gymnocladus dioicus  Kentucky coffeetree
Ilex opaca  American holly
Juniperus saliciola  Southern red cedar
Juniperus virginiana  Eastern red cedar
Kalopanax pictus  Castor-aralia
Liquidambar styraciflua  Sweetgum
Maclura pomifera  Osage-orange
Magnolia grandiflora  Southern magnolia
Metasequoia glyptostroboides  Dawn redwood
Nyssa ogeche  Ogeche gum
Oxydendrum arboreum  Sourwood
Phellodendron amurense  Amur cork tree
Picea glauca  Alberta spruce
Picea pungens  Colorado blue spruce
Pinus bungeana  Lacebark pine
Pinus cembra  Swiss stone pine
Pinus echinata  Shortleaf pine
Pinus elliottii  Slash pine
Pinus flexilis  Limber pine
Pinus heldreichii  Bosnian pine
Pinus koraiensis  Korean pine
Pinus mugo  Mugo pine
Pinus nigra  Austrian pine
Pinus rigida  Pitch pine
Pinus sylvestris  Scotch pine
Pinus taeda  Loblolly pine
Pinus thunbergiana  Japanese black pine
Pinus virginiana  Virginia pine
Pinus wallichiana  Himalayan pine
Platanus acerifolia  London plane tree
Pyrus calleryana   Callery pear
Quercus acutissima  Sawtooth oak
Quercus alba  White oak
Quercus bicolor  Swamp white oak
Quercus coccinea  Scarlet oak
Quercus falcata  Southern red oak
Quercus hemisphaerica  Darlington oak
Quercus imbricaria  Shingle oak
Quercus lyrata  Overcup oak
Quercus macrocarpa  Bur oak
Quercus nigra  Water oak
Quercus nuttalii  Nuttall oak
Quercus palustris  Pin oak
Quercus phellos  Willow oak
Quercus prinus  Chestnut oak
Quercus rubra  Red oak
Quercus shumardii  Shumard oak
Quercus stellata  Post oak
Quercus virginiana  Live oak
Robinia pseudoacacia  Black locust
Sassafras albidum  Sassafras
Taxodium ascendens  Pond cypress
Taxodium distichum  Baldcypress
Tilia americana  American linden
Tilia cordata  Littleleaf linden
Tilia tomentosa  Silver linden
Ulmus alata  Winged elm
Ulmus americana   American elm
Ulmus parvifolia  Lacebark elm
Zelkova serrata  Zelkova

Small Drought Tolerant Trees 
Botanical Name      Common Name    
Acer barbatum   Southern sugar maple
Acer buergeranum  Trident maple
Acer campestre  Hedge maple
Acer ginnala  Amur maple
Acer leucoderme  Whitebark maple, calk maple
Acer negundo  Boxelder
Acer truncatum  Purple blow maple
Aesculus californica  California buckeye
Aesculus pavia  Red buckeye
Albizia julibrissin  Mimosa
Alnus japonica  Japanese alder
Alnus serrulata  Tag alder
Carpinus betulus  European hornbeam
Carpinus betulus fastigiata  Upright European hornbeam
Carpinus caroliniana  American hornbeam, Ironwood
Carpinus japonica  Japanese hornbeam
Carpinus orientalis  Oriental hornbeam
Cercis canadensis  Eastern redbud
Cercis canadensis ssp retisus  Oklahoma redbud
Cercis canadensis ssp. texensis  Texas redbud
Cercis chinensis  Chinese redbud
Chionanthus retusus  Chinese fringe tree
Cornus mas  Cornelian Cherry dogwood
Cotinus coggygria  Smoketree
Cotinus obovatus  American smoke tree
Crataegus crus-galli  Cockspur hawthorn
Crataegus crus-galli inermis Crusader hawthorn
Crataegus laevigata  Scarlet hawthorn, English hawthorn
Crataegus phaenopyrum  Washington hawthorn
Crataegus x lavallei  Lavalle hawthorn
Crataegus viridis  Green hawthorn
Cupressus sempervirens  Italian cypress
Cydonia sinensis  Chinese quince
Cupressus arizonica cvs.  Arizona cypress
Elaeagnus angustifolia  Russian olive
Euscaphis japonica  Korean sweetheart tree
Heptacodium miconiodes  Seven-son flower
Hovenia dulcis  Japanese raisin tree
Ilex x merserveae  Merserve hybrid hollies
Ilex cassine  Dahoon holly
Ilex cornuta   Chinese Holly
Ilex decidua  Possumhaw
Ilex latifolia  Lusterleaf holly
Ilex pedunculosa  Long stalk holly
Ilex vomitoria  Yaupon holly
Ilex x ‘Emily Bruner’  Emily Bruner holly
Ilex x ‘Mary Nell’  Mary Nell holly
Ilex x 'Nellie R. Stevens'  Nellie R. Stevens holly
Ilex x attenuata  Savannah, Foster, Sunny Foster, East Palatka
Ilex x koehneana  Koehne holly
Juniperus scopulorum  Rocky Mountain juniper
Juniperus virginiana  Eastern Redcedar
Juniperus chinensis  Chinese juniper
Koelreuteria bipinnata  Goldenraintree
Koelreuteria paniculata  Goldenraintree
Lagerstroemia fauriei  Japanese crapemyrtle
Lagerstroemia indica  Crapemyrtle
Lithocarpus henryi  Henry tanbark oak
Ilex vomitoria 'Pendula'  Weeping yaupon holly
Maackia amurensis  Amur Maackia
Maclura pomifera   Osage Orange
Magnolia grandiflora ‘Little Gem’  Little Gem magnolia
Magnolia hybrids  Magnolia
Malus hybrids  Crabapple
Malus spp.  Crabapple
Morus australis ‘Unryo’  Contorted mulberry
Ostrya virginiana  American hophornbeam or ironwood
Oxydendrum arboreum  Sourwood
Parrotia persica  Persian ironwood
Persea borbonia  Redbay
Photinia serrulata  Chinese photinia
Picea glauca  Conica (dwarf cultivars)
Picea pungens Colorado Spruce
Pinus mugo  Mugo pine
Pinus nigra   Austrian Pine
Pinus rigida  Sherman Eddy
Pinus strobus cvs.  Eastern White pine
Pinus thunbergiana cvs.  Japanese Black Pine
Pistacia chinensis  Chinese pistache
Poncirus trifoliata Hardy orange
Ptelea trifoliata  Hop tree
Pyrus calleryana   Callery Pear
Quercus muehlenbergii   Chinkapin Oak
Rhamnus caroliniana  Carolina buckthorn
Rhus typhina  Staghorn sumac
Trachycarpus fortunei  Windmill palm
Ulmus glabra ‘Horizontalis’  Tabletop Scotch elm
Vitex agnus-castus  Chastetree; vitex
Ziziphus jujuba  Common jujuba
                                                      Trees that Tolerate Heat

High temperatures have a detrimental effect on tree leaves and roots.  Increased leaf temperatures cause trees to cool themselves through the process of transpiration.  As temperatures rise, water vapor is released through stomata in the leaf surface, thereby cooling the tree.  On a hot day, a large deciduous tree can transpire as much as 100 gallons (400 liters) of water into the surrounding air.  This volume of water is not always available to trees on hot sites because of inadequate moisture in the soil.  A lack of available water for trees in hot sites often results in scorched leaf margins or dead leaves.

High temperatures can adversely affect roots.  Optimum tree root growth occurs when soil temperatures are between 60° F (15° C) and 80° F (26° C).  When soil temperatures exceed 86° F (30° C), roots cannot function and begin to die.  The loss of vital roots and their uptake of water and dissolved nutrients can result in tree death.

Hot Site Characteristics
A variety of different locations and situations qualify as hot landscape sites.  Hot site characteristics include:
  • large masses of asphalt and concrete that absorb and reflect heat,
  • urban areas that tend to be an average of 9° F to 12° F (5° C to 9° C) warmer than surrounding wooded areas,
  • heat that continues to radiate even after sunset from buildings and roads, 
  • areas adjacent to buildings that tend to be hot because buildings reflect heat onto trees next to southern and western walls,
  • automobile surfaces that can exceed 122° F (50° C) during the summer,
  • heat being released from car fumes any time, day or night,
  • underground utilities such as steam lines produce heat all the time,
  • containers and raised beds get hotter than in-the-ground planting areas,
  • open areas, such as athletic fields and meadows, are hotter than wooded areas where trees provide shade.

Hot landscape sites require special consideration before trees are installed.  Trees can survive, and even thrive, in hot sites if:
  • the soil is prepared correctly,
  • heat-tolerant species are selected,
  • the trees are properly watered and maintained. 

Prepare Hot Installation Sites
Preparation prior to tree installation is important to help trees adjust to hot sites.  If large planting beds will be used, organic matter such as compost should be incorporated into the soil to improve soil structure, air movement, and water retention.  Incorporation of organic matter into the backfill soil for only individual planting holes is not recommended.

Installation of an irrigation system may be beneficial because irrigation can supply water for transpirational cooling.

Trees for Hot Sites
Trees that are genetically capable of tolerating high temperatures should be selected for hot sites.  Some species of trees are naturally heat-resistant, and many cultivars are available that were found growing in hot deserts and have been selected for their ability to withstand high temperatures.  Consideration should be given to site moisture levels because some trees can withstand heat only when adequate moisture is available.

Some trees, such as Box Elder (Acer negundo), Tree-of-Heaven (Ailanthus altissima), and Black Locust (Robinia pseudoacacia) are heat tolerant and, if found growing on a site, should be considered for retention.  Otherwise they are not considered to be desirable landscape trees due to insect problems and/or invasive growth.

Follow-up Care
After heat-tolerant trees have been installed, in the right soil, additional maintenance is needed to ensure long-term tree health. 
  • Trees should receive 1" (2.5 cm) of water per week during the growing season to replace water lost through transpiration.
  • Add water slowly and deeply and include areas beyond the tree's dripline where small absorbing roots are located.
  • Maintain a 2” – 4" (5 – 10 cm) layer of mulch over as much of the tree's root zone as possible.  Mulch will help keep the soil surrounding the roots cooler, prevent moisture evaporation and water runoff, minimize competing weed growth, and reduce the amount of light and heat that reflects onto leaf and stem surfaces.
  • Biochar is recommended if a soil amendment is desired.  This product may allow the tree to find moisture and minerals beyond what the tree roots will normally be able to absorb. 
  • Fertilize trees in hot sites only as needed.  Nitrogen causes trees to grow quickly, and an extra flush of new leaves may wilt and die due to heat stress. 
  • Perform soil testing.  Observe plant health care to determine if and when supplemental fertilization is needed.
  • Prune trees as necessary to remove broken, diseased, damaged, or leggy growth.  Pruning improves overall tree health, reduces water demand, and decreases the amount of water that is lost due to transpiration. 
  • In summer, shade newly installed trees with netting or boards until their roots become established and capable of absorbing adequate water for transpiration. 
  • Leaves on trees transplanted during summer heat, or into hot sites, are sometimes sprayed with antitranspirants to successively prevent excessive water loss during transporting. 
  • In extreme heat, keep the tree heavily watered and spray water on the leaves.

Trees for Hot Sites 
Botanical Name   Common Name
Acer buergeranum  Trident maple
Acer campestre  Hedge maple 
Acer platanoides  Norway maple 
Acer rubrum  Red maple 
Acer saccharum  Sugar maple 
Acer x freemanii  Freeman maple 
Aesculus x carnea  Red horsechestnut
Betula nigra  River birch 
Betula platyphylla  White birch 
Catalpa speciosa   Catalpa 
Celtis occidentalis  Common hackberry 
Crataegus crusgalli  Cockspur hawthorn 
Crataegus phaenopyrum  Washington hawthorn 
Cryptomeria japonica  Japanese cryptomeria 
Cupressocyparis leylandii  Leyland cypress
Eucommia ulmoides  Hardy rubber tree 
Fraxinus americana  White ash  (Use in non-EAB areas only)
Fraxinus pennsylvanica  Green ash  (Use in non-EAB areas only)
Ginkgo biloba  Ginkgo   (male trees only)
Gleditsia triacanthos  Honeylocust
Juniperus chinensis  Chinese juniper  
Juniperus scopulorum  Rocky mountain juniper
Juniperus virginiana  Eastern redcedar
Koelreuteria paniculata  Goldenraintree
Lagerstroemia spp.  Crape myrtle 
Liquidambar styraciflua  Sweetgum 
Myrica cerifera  Waxmyrtle 
Picea pungens  Colorado spruce 
Pistacia chinensis  Chinese pistache 
Platanus x acerifolia  London planetree 
Podocarpus macrophyllus  Chinese podocarpus 
Prunus ceracifera  Pissard plum
Prunus x yedoensis  Yoshino cherry 
Pyrus calleryana  Callery pear   Avoid ‘Bradford’
Quercus hemisphaerica  Laurel oak 
Quercus phellos  Willow oak 
Quercus robur  English oak 
Quercus rubra  Red oak 
Quercus virginiana  Live oak 
Sophora japonica  Japanese pagodatree 
Thuja occidentalis  American arborvitae 
Thuja orientalis  Oriental arborvitae 
Tilia cordata  Littleleaf linden 
Tilia tomentosa  Silver linden 
Ulmus parvifolia  Lacebark elm 
Vitex agnus-castus  Chastetree 
Zelkova serrata  Japanese zelkova 

The nursery industry has developed cultivars of most of the trees listed above.  These cultivars are usually selected because they are more attractive, disease resistant, or tolerant of adverse growing conditions.  Therefore they will grow into better trees in hot situations than the species and in general, should be considered instead of the species.  For an updated list of these cultivars and species, see 'A Solution to Global Warming'   
                                             Trees That Tolerate Low Soil Oxygen

Compacted and poorly-drained soils contain less oxygen than tree roots require in order to survive and grow.  Trees subjected to long periods of flood water over their roots or extremely wet or compact soils will suffer, not from the water, but from a lack of oxygen in the soil.  In wet soils, too much water in the soil replaces air in the soil pores, resulting in low oxygen levels.  In compact soil the soil pores that would contain oxygen have been crushed.

Many trees die, grow poorly, or succumb from an insect or disease problem, because they are installed in soil that is too wet or lacking in oxygen for them to grow well during certain times of the year.  Only species and cultivars tolerant of wet or compact sites can survive in these difficult soils.  Where soil oxygen is lacking, water and nutrient uptake stops, plant processes and growth cease, and trees and shrubs begin to decline or die. 

Soil Drainage Test
If the soil seems very compact, very wet, or low in oxygen, consider doing a soil drainage or hydraulic test.  Start by digging a narrow hole 12 – 18 inches (30 – 46 cm) deep.  The idea is to make a fairly small hole in the area where the roots will be growing.  Next, get a yardstick and place it in the hole, then fill the hole to the top with water.  As soon as it has all drained out, fill the hole again and this time, count the minutes it takes for the water to drain out of the hole.  If the water level is dropping at 2 inches or more an hour, you do not have a problem with soil compaction.  If the water level is dropping at less than 2 inches an hour, there is a problem that will require looking at the following options.  

The first option to consider is deep aeration to loosen the subsoil.  Another option would be to mix coarse sand into the top 36 inches (90 cm) of topsoil to improve the soil structure.   Approximately 75% sand by volume would need to be added to affect a positive change in drainage.  Any soil improvement effort will also require a means for the excess water to drain away to a lower area.  A third option comes from a recent research effort that required digging a tree installation hole with a backhoe tractor.  The soil is then dropped back into the hole from the bucket raised several feet in the air, with alternating buckets of compost.  This aerates the soil as well as provides micro-organisms and nutrients for the tree to use immediately after the installation.

You will also have to keep the tree mulched with composted organic material and to replenish the compost every year.  The best way to replenish the compost is to maintain a 2 – 3 inch (5 – 8 cm) layer of mulch on the surface of the soil.  Also keep the soil around the installation hole loosened with a shovel, a piped drainage system, or frequent treatments with a pneumatic soil excavating tool or a water spade.

However, simple soil modifications may not be an option.  If a hardpan (a compacted, impermeable layer of soil with an underlying layer of well-drained soil) is present, a hole can be dug down through the hardpan to the permeable layer to provide drainage for the installation hole.  If the soil is poorly drained and there is no well-drained layer below, a perforated pipe system will need to be laid.  This, however, is expensive and requires the assistance of a professional engineer or landscape architect for developing a proper drainage design. This design will require perforated pipes around the tree pit, below the root ball and connected to the storm drain system.  The perforated pipe should be laid in a gravel-filled trench.  A second design option is the construction of a French drain, which is a gravel filled trench.  The French drain must also exit at a city storm drain.  Simply adding gravel to the bottom of the installation hole will further decrease oxygen availability to the root system and this effort will not solve the problem. 

Also, consider installing the trees above the existing soil as a large mound or raised bed with up to one third of the root ball above grade.  Since poor soil is frequent in urban landscapes, consider using something such as CU-Structural Soil™  or soil cells as well as installing trees from the list below that tolerate very poor and constantly wet soil.
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Tree List
After all efforts to correct the drainage problem have been made, select trees that tolerate low soil oxygen levels from the list that follows:

Trees that Tolerate Low Soil Oxygen
Botanical Name    Common Name
Acer negundo  Boxelder
Acer rubrum   Red maple
Acer saccharinum   Silver Maple
Aesculus hippocastanum   Common Horsechestnut
Alnus glutinosa   European Alder
Betula nigra   River Birch
Carpinus caroliniana   American Hornbeam
Carya laciniosa   Shellbark Hickory
Crataegus spp.   Hawthorn
Diospyros virginiana   Persimmon
Fraxinus americana   White Ash (use in non-EAB areas only)
Fraxinus pennsylvanica   Green Ash (use in non-EAB areas only)
Fraxinus profunda   Pumpkin Ash
Gleditsia aquatic   Water Locust
Gleditsia triacanthos var. inermis  Honeylocust
Ilex opaca    American Holly
Juniperus virginiana   Eastern Red Cedar
Larix decidua    European Larch
Larix laricina    American Larch
Liquidambar styraciflua   Sweetgum
Nyssa sylvatica    Tupelo
Nyssa aquatic   Water Tupelo
Ostrya virginiana   American Hophornbeam
Planera aquatic   Waater Elm
Plantanus acerifolia    London Planetree
Plantanus occidentalis   Sycamore
Populus deltoides   Eastern Cottonwood
Quercus bicolor   Swamp White Oak 
Quercus imbricaria   Shingle Oak
Quercus lyrata    Overcup Oak
Quercus palustris  Pin Oak
Quercus phellos   Willow Oak
Salix spp.        Willow
Sassafras albidum   Common Sassafras
Taxodium distichum   Common Baldcypress

The nursery industry has developed cultivars of most of the trees listed above.  These cultivars are usually selected because they are more attractive, disease resistant, or tolerant of adverse growing conditions.  Therefore they will grow into better trees in urban situations than the species and should be considered instead of the species.
                                                  Trees That Tolerate Air Pollution

Polluted air is a major stress that contributes to the decline of urban trees.  Air pollution may cause acute (short-term) damage, which is immediately visible, and chronic (long-term) damage, which can lead to gradual tree decline.  Chronic damage may predispose trees to other disorders as well, thus making diagnosis of the real problem difficult.

Weather and Pollutants
Under normal conditions, warm air near the soil surface causes the air currents to rise vertically carrying the pollutants with them.  The pollutants rapidly become diluted and are blown away by upper level winds before coming into contact with most trees.  However, thermal inversions (cool air at the surface beneath warmer air above) restrict air movement and force the dispersal of pollutants down to the ground surface, resulting in increasing phytotoxic levels and prolonged exposure that results in damage to trees and tree growth.     

Temperature also influences a pollutant's chemical reaction rate.  When the temperature is high, more photo-chemical oxidants are produced.  These oxidants cause more severe damage during hot, sunny weather and less damage during cool, cloudy weather.  Atmospheric moisture causes these pollutants to become solutions, thereby increasing their toxic potential as the so-called "acid rain".  

Gaseous Pollutants
Gaseous pollutants, such as ozone and sulfur dioxide, enter trees through leaf stomates and react within leaf tissues to inhibit photosynthesis.  Acute levels can be high enough to cause sudden tissue damage and cell death.  Chronic damage occurs when small amounts of toxic gases enter leaves and do not initially cause tissue death, but inhibit leaf functions.  Whether or not a pollutant causes acute or chronic damage depends upon the tree species and its tolerance to the pollutant toxicity.  Individual trees within a species often display varying degrees of tolerance to the same pollutant.  This sometimes results in cultivars being selected by scientists and plant breeders that are much more tolerant of air pollution than the species.

Ozone
Ozone is the most damaging air pollutant.  The action of sunlight (ultraviolet radiation) on molecular oxygen and oxides of nitrogen spontaneously generate ozone.  The organic compounds in automobile exhaust enhance ozone accumulation.  The extent of tree damage depends on the concentration of ozone, the duration of the exposure, and the tree's sensitivity. 

Acute ozone damage to deciduous trees causes:
  • marginal leaf burn and dot-like or irregularly shaped lesions or spots that may be tan, white, or dark brown, and they may spread over the entire leaf surface,
  • bleaching of the leaf's upper surface, 
  • conifer browning at the same point on all needles in a needle cluster,
  • increases in a tree's susceptibility to insect damage. 

Sulfur Dioxide
Sulfur dioxide is primarily a result of fossil fuel burning for electricity generation, and to a lesser degree, the processing of steel and other ores.  Acute sulfur dioxide damage causes severe leaf scorch, usually on upper interveinal leaf surfaces, leaf discoloration (colors ranging from white to red), and tree decline. Younger leaves are generally more sensitive.  Moisture in the air or on leaf surfaces may combine with sulfur dioxide to form sulfuric acid.  Sulfuric acid causes leaf scorch, spotting defoliation, and can also cause tree death over a large geographic area with many affected species. 

Particulates
Particulates or dusts are generated by major industrial processes and auto exhaust emissions.  Particulates are not extremely damaging, but can inhibit or reduce photosynthesis by plugging the stomates on the leaf surface.  Particulates are usually washed off from leaves by rain or irrigation, and therefore they are more harmful during dry periods.

Diagnosing Air Pollution Damage
Proper diagnosis of air pollution damage is difficult because other causes of tree damage, including insects and diseases, can cause similar symptoms.  Obtaining the following information will help in making a proper diagnosis:
  • pollutant origin,
  • chemical and physical nature of the pollutant,
  • geographic and topographic influences,
  • weather conditions,
  • length of exposure and concentration,
  • types of symptoms,
  • possible mimicking symptoms,
  • size of affected area,
  • date of suspected exposure,
  • affected tree and other species,
  • history of previous exposure.

Trees with a Tolerance to Air Pollution
Botanical name    Common Name 
Abies balsamea    Balsam fir
Abies concolor    White fir
Acer saccharum    Sugar maple
Betula pendula    European white birch
Cercis canadensis    Eastern redbud
Cornus florida    Flowering dogwood
Ginkgo biloba    Ginkgo
Ilex spp.   Holly
Juglans nigra    Black walnut
Lagerstroemia speciosa   Crapemyrtle
Nyssa sylvatica   Black gum
Picea abies    Norway spruce
Picea pungens   Blue spruce
Pinus echinata    Shortleaf pine
Pinus resinosa    Red pine
Pseudotsuga menziesii    Douglas fir
Quercus robur    English oak
Quercus rubra    Red oak
Taxus spp.   Yew
Thuja spp.   Arborvitae
Tilia cordata    Little-leaf linden

Trees with a Tolerance to Sulfur Dioxide
Botanical name     Common Name 
Acer saccharinum  Silver maple
Acer saccharum  Sugar maple
Ginkgo biloba  Ginkgo
Juniperus spp.  Juniper
Picea pungens  Blue spruce
Quercus palustris   Pin oak
Quercus rubra  Red oak
Thuja spp.   Arborvitae
Tilia cordata   Littleleaf linden
Taxodium distichum   Common Baldcypress

The nursery industry has developed cultivars of most of the trees listed above.  These cultivars are usually selected by plant breeders because they are more attractive, disease resistant, or tolerant of adverse growing conditions.  Therefore they will grow into better trees in urban situations than the species and should be considered instead of the species.
                                              Trees That Tolerate Salt Damage

Although sodium chloride assists in keeping pavements dry and safe during ice and snow, their extensive use can cause damage to trees along streets and highways.  Many trees can be disfigured and killed by sodium chloride.  The worst damage occurs to sensitive species growing near roads during winters when excessive snow or ice has been treated with sodium chloride.  The salt level in soils may also be elevated because of excessive fertilizer levels or irrigation water that is high in soluble salts.  This problem is worse in areas with low rainfall and extensive use of irrigation and fertilizer.  A soil that is high in salts will have less water available for the roots of trees and other plants. 

Sodium reduces the uptake of potassium, calcium, and magnesium by displacing those nutrients.  Excessive sodium in soil causes soil aggregates to break down, resulting in poor aeration and slow water permeability.  The resulting soil lacks good drainage and proper oxygen concentrations and leads to reduced moisture uptake by roots.  High levels of salt can sometimes reverse the flow of liquids in the tree and draw moisture out of the roots. 

Fortunately many highway departments are reducing their applications of sodium chloride and switching to less toxic products such as calcium chloride and various brines that are less damaging to plants while still keeping the roads safe for vehicles.  This has reduced the sodium damage to trees in some cities, but it has not eliminated the problem.

Symptoms
On deciduous trees, those with thin bark, such as beech, are highly susceptible.  Trees with resinous buds, such as cottonwood, are fairly resistant to injury, as are trees whose buds are submerged in the twig, such as black locust and honeylocust.  Generally, plants with naked buds are injured more than trees with scaly buds.  Look for "witch's-brooms" on deciduous trees or yellow, brown, or fallen needles on evergreens to identify winter salt damage. 

Foliar damage from salt spray normally occurs on the windward side of the tree but in severe cases the whole tree may be affected.  Yew, arborvitae, and hemlock are most susceptible, but winter browning can affect all evergreens.  New transplants or trees with succulent, late season growth are also sensitive.

Treatments
The use of salt tolerant trees is the best means of treatment.  The next best treatment is to use calcium chloride as a substitute for sodium chloride and various brines.  However this treatment is very expensive but many cities are combining a mix of favorite local products to provide a longer treatment period with less sodium usage.  Another treatment that works well is to flush the sodium out of the soil in spring, before growth starts.  Usually spring rains provide this treatment, but in high value landscapes it may have to be done by the arborist or landscape architect applying excessive irrigation water. 

Other treatments that work well in certain locations include applying gypsum (calcium sulfate).  The calcium displaces the sodium and this improves the soil drainage and aeration.  There are other potential treatments such as installing susceptible trees further than 60 feet away from the road and installing the trees in a raised bed.

If a tree is to be located at a site susceptible to wind-blown salt, select a species from the list that follows:

Trees Tolerant to Salt Spray on Leaf Surfaces 
Botanical name      Common Name 
Acer campestre   Hedge maple  
Acer platanoides  Norway maple  
Acer pseudoplatanus  Sycamore maple
Acer saccharinum  Silver maple  
Aesculus spp.   Buckeye  
Aesculus hippocastanum Horsechestnut  
Ailanthus altissima  Tree of heaven, Ailanthus
Amelanchier spp.  Shadblow, serviceberry 
Asimina triloba   Pawpaw  
Betula spp.   Birch  
Carya spp.   Hickory/pecan 
Casuarina equisetifolia  Australian pine  
Catalpa spp.   Catalpa   
Cercidiphyllum japonicum  Katsura tree   
Chionanthus virginicus  White fringe tree 
Cladrastis lutea   American yellowwood 
Clusia rosea   Pitch apple  
Cocos nucifera   Coconut palm  
Conocarpus erecta  Buttonwood  
Cornus florida   Flowering dogwood 
Cupaniopsis anacardioides  Carrotwood  
Diospyros virginiana  Common persimmon 
Elaeagnus angustifolia  Russian olive 
Fraxinus spp.   Ash 
Fraxinus quadrangulata  Blue ash 
Ginkgo biloba   Ginkgo, maidenhair tree 
Gleditsia triacanthos  Common honey locust  
Gymnocladus dioicus  Kentucky coffeetree 
Ilex opaca   American holly   
Jacaranda mimosaefolia  Jacaranda   
Juglans spp.   Walnut/butternut  
Juniperus spp.   Juniper   
Koelreuteria paniculata   Goldenraintree   
Laburnum x watereri  Goldenchain tree   
Larix deciduas   European larch  
Liquidambar styraciflua   Sweetgum   
Maclura pomifera  Osage orange   
Magnolia spp   Magnolia    
Malus spp.   Apple, crabapple  
Morus spp.   Mulberry   
Nyssa sylvatica   Tupelo, blackgum, sourgum 
Ostrya virginiana  Hophornbeam, ironwood 
Oxydendrum arboreum   Sourwood  
Paulownia tomentosa  Paulownia    
Persea borbonia  Redbay    
Phellodendron spp.  Corktree   
Picea glauca   White spruce  
Picea pungens   Colorado spruce  
Pinus nigra   Austrian pine 
Platanus spp.   Plane tree/ sycamore 
Populus spp.   Poplar   
Prunus spp.   Cherry/plum  
Pseudolarix amabilis  Golden larch  
Pseudotsuga menziesii  Douglas-fir  
Pyrus calleryana  Callery pear  
Quercus alba   White oak  
Quercus bicolor   Swamp white oak
Quercus imbricaria  Shingle oak  
Quercus macrocarpa  Bur oak   
Quercus palustris  Pin oak   
Quercus phellos  Willow oak   
Quercus robur   English oak   
Quercus rubra   Red oak    
Quercus velutina  Black oak  
Quercus virginiana  Live oak    
Rhamnus cathartica  Common buckthorn  
Robinia spp.   Locust    
Sabal palmetto   Cabbage palm  
Salix spp.   Willow   
Sassafras albidum  Sassafras   
Sophora japonica  Japanese pagodatree 
Sorbus spp.   Mountain ash  
Syringa pekinensis  Pekin lilac 
Taxodium spp.   Cypress 
Taxus spp.   Yew   
Ulmus spp.   Elm   
Ulmus pumila   Siberian elm  

If the soil has a naturally high salt content from winter de-icing or proximity to a salt water body, select a tree from the list that follows:

Trees Tolerant to Salt in the Soil 
Botanical name       Common Name 
Acer campestre   Hedge maple   
Acer platanoides  Norway maple   
Acer saccharinum  Silver maple   
Aesculus hippocastanum Horsechestnut   
Ailanthus altissima  Tree of heaven, Ailanthus 
Clusia rosea   Pitch apple   
Cocos nucifera   Coconut palm  
Conocarpus erecta  Buttonwood   
Cornus florida   Flowering dogwood  
Crataegus spp.   Hawthorn
Cupaniopsis anacardioides  Carrotwood  
Elaeagnus angustifolia  Russian olive   
Fraxinus spp.   Ash    
Ginkgo biloba   Ginkgo, maidenhair tree 
Gleditsia triacanthos  Common honey locust  
Juglans spp.   Walnut/butternut  
Juniperus spp.   Juniper    
Koelreuteria paniculata   Goldenraintree   
Laburnum x watereri  Goldenchain tree   
Larix decidua   European larch   
Morus spp.   Mulberry   
Persea borbonia  Redbay    
Picea pungens   Colorado spruce   
Pinus nigra   Austrian pine
Pinus thunbergiana  Japanese black pine 
Populus spp.   Poplar    
Quercus alba   White oak   
Quercus robur   English oak   
Quercus rubra   Red oak   
Quercus virginiana  Live oak    
Rhamnus cathartica  Common buckthorn  
Robinia spp.   Locust    
Sabal palmetto   Cabbage palm   
Salix spp.   Willow     
Syringa pekinensis  Pekin lilac  
Taxodium spp.   Cypress   
Ulmus pumila   Siberian elm   
                                        Trees That Tolerate Compacted Urban Soils

In order to develop a list of trees that do well in compacted urban soils, researchers studied trees that do well in the worst-case natural soils – clay.  Selection and improvement of trees tolerant of clay become trees of great importance in coping with compacted urban soils.  Springtime wetness is a major stress-maker for trees installed in compacted material.  Poor aeration is associated with rootlets failing to develop.  This leads to transpiration stress in mid-summer because of impaired water uptake capacity.  Also, proper nutrient uptake may be affected.  Installing a tree in compacted soil is essentially the same as installing one in a large container without a drain-hole.

Making Improvements to Compacted Soil                                                                                                              
Some guidelines to improving urban tree installation sites might include:
  • install on slopes rather than on flat areas where water may stand,
  • install on a raised mound with one third the rootball, above grade,
  • make sure that settling will not create a depression around the tree,
  • prepare a hole with an extensive width to promote proliferation of roots in the top six inches where aeration is most favorable,
  • use mulches for moderating moisture and temperature levels of the mulched area and for reducing grass or weed competition,
  • areas with soil profiles intact should be preserved if at all possible, to utilize a more favorable planting
    medium.

Trees that Should Do Well in Compacted Urban Soils
Consideration of ways to lessen the limitations of a compacted soil is second in importance to the successful selection of certain species of trees.  For example, floodplain and swamp species are generally successful urban trees.  Not only do these species tolerate spring wetness but they also do well with compacted soils.  A few of the trees listed below are considered invasive and are not acceptable in many cities.  Most of the trees listed have excellent cultivars available that should be selected instead of the species.  Before selecting any of the trees listed below, be sure all the other factors of tree and site quality are suitable for tree growth.  In other words “grow the right tree, in the right place, for the right reason”.

Trees for Compacted Urban Soils 
Botanical Name   Common Name
Acer ginnala  amur maple 
Acer campestre  hedge maple
Acer negundo  boxelder  (single stem forms)
Acer nigrum  black maple 
Acer platanoides  Norway maple 
Acer rubrum red maple 
Aceer saccharinum  silver maple  (single stem forms)
Acer saccharum  sugar maple
Alnus glutinosa  European black alder
Betula maximowicziana monarch birch  
Betula nigra  river birch
Callistemon viminalis  weeping bottlebrush 
Celtis occidentalis  hackberry
Crataegus crus-galli  cockspur hawthorn
Crataegus phaenopyrum  Washington hawthorn 
Fraxinus excelsior  Hesse European ash   (plant only in non-EAB areas)
Fraxinus guadrangulata  blue ash    (plant only in non-EAB areas)
Fraxinus pennsylvanica  green ash   (plant only in non-EAB areas)  
Fraxinus tomentosa  pumpkin ash   (plant only in non-EAB areas)  
Gleditsia triacanthos inermis  honeylocust 
Larix decidua European larch
Melaleuca linariifolia  flaxleaf paperbark 
Nyssa sylvatica  sour gum
Pinus flexilis  limber pine 
Pittosporum undulatum  Victorian box 
Populus deltoides  cottonwood  (single stem forms) 
Quercus bicolor  swamp white oak 
Quercus macrocarpa  bur oak 
Quercus muehlenbergii   chinquapin oak 
Quercus palustris  pin oak  (plant only in acidic areas)
Quercus rubrum  northern red oak 
Quercus shumardii  Shumard oak 
Quercjus texana  Texas red oak  
Salix nigra  black willow
Taxodium distichum  baldcypress
Thuja occidentalis  northern white cedar
Tilia cordata  linden   (select ‘Greenspire’‘Redmond’ cultivars)
Ulmus americana  American elm 
Ulmus japonica  Japanese elm 
Ulmus parvifolia  lacebark elm   
                                                Trees That Tolerate High pH

Soil pH (potential Hydrogen) is a measure of soil acidity or alkalinity.  The balance between hydroxyl and hydrogen ions determines pH.  Soil pH is important because it affects the availability of plant nutrients, toxic elements, and soil microbes. 

A soil pH of 0 – 7 is acidic soil while a soil pH of 7 – 14 is an alkaline soil.  A pH of 7 is neutral.  Many woody plants will actually be able to survive in soils with a wide range of pH, from about 4.5 – 8.2.  But for optimal health and growth, most trees and shrubs do best with a soil pH of 6.0 – 7.0.  The exception is acid-loving plants which prefer a lower pH of 4.5 – 6.0. 

It is important to identify alkaline-tolerant trees because many urban soils are high in pH.  Concrete sidewalks, underground drain pipes, building foundations, broken up concrete solid fill, and other calcium-based construction materials, contribute to alkaline urban soil conditions and raise the soil pH.  These construction materials are considered non-hazardous and can therefore be used as solid fill and placed as backfill for buildings or bases under roads and sidewalks (often in the same locations where trees are to grow). 
​
Some species of trees need an alkaline soil, but most species can not tolerate a high pH level.  A high pH may also cause chemical reactions with nutrients in the soil that render the nutrients unavailable to the tree.  Iron, for example, becomes unavailable for a tree’s growth processes when soil pH is alkaline.  Sulfur may be added to the soil to lower the pH, but this effort usually results in only a temporary lowering of the pH.  Tolerance to the local soil conditions needs to be considered when selecting a tree to install in an urban area.  Be sure to take a soil test to see if these high pH-tolerant trees would be appropriate.

The trees listed below prefer a pH of 6.0 – 7.0, but will still perform admirably under alkaline soil conditions up to a pH of 8.2. 

Botanical name     Common Name 
Acer platanoides    Norway Maple
Aesculus x carnea   Red Horsechestnut
Carpinus betulus   European Hornbeam
Catalpa speciosa   Northern Catalpa
Celtis occidentalis   Common Hackberry
Cercidiphyllum japonicum   Katsura
Cercis canadensis   Eastern Redbud
Cladrastis kentukea  Yellowwood
Corylus colurna   Turkish Filbert
Cotinus obovatus  Smoketree
Crataegus spp.  Hawthorn
Eucommia ulmoides  Hardy Rubber Tree
Ginkgo biloba   Ginkgo
Gleditsia triacanthos   Honeylocust
Gymnocladus dioicus   Kentucky Coffeetree
Juniperus virginiana   Eastern Red Cedar
Koelreuteria paniculata   Goldenraintree
Liriodendron tulipifera   Tulip Tree
Maackia amurensis   Amur Maackia
Maclura pomifera   Osage Orange
Malus spp.   Crabapple
Metasequoia glyptostroboides   Dawn Redwood
Ostrya virginiana   American Hophornbeam
Parrotia persica   Persian Parrotia
Platanus x acerifolia   London Planetree
Quercus macrocarpa   Bur Oak
Quercus muehlenbergii  Chinkapin Oak
Quercus robur   English Oak
Quercus shumardii   Shumard Oak
Sorbus alnifolia   Korean Mountainash
Styphnolobium japonicum  Japanese Pagodatree
Syringa reticulata   Japanese Tree Lilac
Tilia spp.   Linden
Ulmus americana   American Elm
Ulmus parvifolia   Lacebark Elm
Zelkova serrata   Japanese Zelkova

The nursery industry has developed cultivars of most of the trees listed above.  These cultivars are usually selected because they are more attractive, disease resistant, or tolerant of alkaline soil.  Therefore they will grow into better trees in urban situations than the species and should be considered instead of the species.
                                              Trees That Tolerate Low Soil Fertility

Low soil fertility can often be an issue in the urban landscape.  Soils in urban areas may also have a nutrient imbalance.  When it is determined that there are inadequate nutrients, tree growth and development will be affected.  Nutrient imbalances are often caused by excessive salts, soil compaction, air pollution, drought, heat, and a high pH.  However, low soil fertility is generally an issue with an individual tree rather than a larger environmental issue and no particular genus or species of trees are known to be tolerant to cases of low soil fertility.  Therefore, there is no list of trees that tolerate low soil fertility.

Low Soil Fertility
Common causes of low soil fertility in urban environments can be for any of the reasons described below:
  • Topsoil and organic matter are often removed from a site during construction so the natural replacement of nutrients by microorganisms can not proceed.
  • Leaves are removed from the soil surface and are not allowed to decompose, which reduces the amount of microorganisms, nitrogen, phosphorus, and other nutrients to replenish the soil.
  • Biological components and microorganisms are not as common in urban soils, which limit soil aeration and the addition of nutrients and organic matter into the soil.
  • Changes in soil chemistry may influence the availability of soil nutrients, interrupting the nutrient cycling process.
​
Correcting these low fertility issues will allow trees to grow at a rate that is typical of the species.
                                              Trees That Tolerate Most Common Pests

Despite providing our trees with all their necessities, insects still cause problems.  The reality is that all trees must die sometime in the future and the leading causes of death are pests, disease, and high winds.  It is the arborist's job to extend the life of healthy, structurally sound trees, for as long a period of time as possible.

In most cases, however, healthy mature trees are able to defend themselves against minor insect exposure without human intervention.  However, if a tree is subjected to repeated defoliation by insects, it can stress the tree and make it more susceptible to infestation by other insects and diseases.  Insects are less likely to attack healthy trees although severe, repeated infestations may warrant treatment.

Trees that are Resistant to Common Pests 
Botanical name     Common Name 
Acer campestre  Hedge Maple
Acer griseum     Paperbark Maple
Acer truncatum  Shantung Maple
Ailanthus altissima  Tree of Heaven
Cercidophyllum japonicum  Katsura
Cladrastis kentukea  American Yellowwood
Crataegus spp.  Hawthorn
Davidia involucrata Dove tree
Ginkgo biloba    Ginkgo
Gymnocladus dioicus  Kentucky Coffeetree
Juniperus scopulorum  'Woodward' Rocky Mountain Juniper
​Koelreuteria paniculata  Goldenraintree
Maclura pomifera  Osage Orange  
Magnolia stellata   Star Magnolia
Magnolia virginiana  Sweetbay Magnolia
Metasequoia  glyptostroboides   Dawn redwood 
Ostrya virginiana    Hophornbeam (Ironwood)
Quercus acutissima  Sawtooth Oak
Quercus muehlenbergii  Chinkapin Oak
Quercus phellos     Willow Oak
Taxodium distichum   Baldcypress
                                     Trees That Tolerate Most Common Diseases

In most cases, healthy mature trees are able to defend themselves against disease exposure without intervention by arborists.  However, if a tree is subjected to repeated defoliation by disease, it can stress the tree and make it more susceptible to infestation by other diseases and insects.  Severe, repeated insect or fungal infestation may warrant treatment.  Many new chemical treatments and techniques to apply them are becoming available to assist the arborist to protect the tree from these problems.  In addition, many new cultivars are being developed with genetic resistance to common diseases. 

Trees that are Resistant to Common Diseases 
Botanical name     Common Name 
Acer griseum   Paperbark maple
Cercidophyllum japonicum  Katsura
Chionanthus virginicus   Fringetree
Cladrastis kentukea   American yellowwood
Cornus kousa   Kousa dogwood
Davidia involucrata Dove tree
Fagus grandifolia   American beech
Fagus sylvatica   European beech
Ginkgo biloba   Ginkgo
Koelreutaria paniculata   Goldenraintree
Liquidambar styraciflua   Sweetgum
Liriodendron tulipifera   Tulip poplar
Maclura pomifera  Osage Orange
Magnolia grandiflora    Southern magnolia
Magnolia stellata   Star magnolia
Magnolia x soulangiana   Saucer magnolia
Magnolia virginiana   Sweetbay magnolia
Metasequoia glyptostroboides   Dawn redwood
Nyssa sylvatica   Black gum
Oxydendrum arboreum   Sourwood
Parrotia persica   Persian parrotia
Pinus bungeana   Lacebark pine
Platanus x acerifolia   London planetree
Quercus phellos   Willow oak
Quercus coccinea   Scarlet oak
Quercus falcata   Southern red oak
Sophora japonica   Japanese pagoda tree
Styrax japonicus   Japanese snowbell
Taxodium distichum   Baldcypress
Tilia americana   American linden
Ulmus parvifolia   Lacebark elm
Zelkova serrata   Japanese zelkova
                                                 The Best of the Urban Tolerant Trees

This section deals with determining the best trees to grow in urban soil and that will tolerate the identifiable environmental issues found in the urban landscape.  The trees described below were determined by selecting the trees from all the previous sections that dealt with very specific urban environment limitations and listing those trees that tolerate five or more of the various constraints. 

All of these trees are well-known by arborists and landscape architects for their tolerance to urban conditions and as such are bordering on being over-used.  However, the selection of cultivars will help lower the risk of a mono-culture landscape.  Those trees with excellent, urban tolerant cultivars have been mentioned at the end of each description.  Many of the trees have other cultivars besides the ones mentioned, but in the opinion of this author, they may not be the best for an urban landscape.  To repeat, nothing beats picking the best tree for the right place and for the right reasons.  There is no one tree that is perfect for all urban environments and urban soils. 

The Trees:
Acer campestre  Hedge Maple – is tolerant of drought, hot sites, compacted urban soil, air pollution, pests, salt spray on the tree surface, salt in the soil, and soils with a high pH.  Hedge maple transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height and width are 25 feet to 35 feet.  Leaves are dark green in summer, yellow in autumn.  The small stature and vigorous growth of hedge maple makes this an excellent street tree for residential areas, and in downtown urban sites.  It is also suitable as a patio or yard shade tree because it creates dense shade.  However, it grows a little too tall for installing beneath some power lines. Fact Sheet   An excellent cultivar to consider is: 'Queen Elizabeth'. Fact Sheet

Acer platanoides  Norway Maple – is tolerant of drought, hot sites, compacted urban soil, air pollution, salt spray on the tree surface, and salt in the soil.  Norway maple transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height and width are 40 feet to 50 feet.  Leaves are dark green in summer, yellow in autumn although there are some cultivars with maroon leaves.  The Norway maple has been very popular and was installed as a street tree, landscape tree and park tree for so many years, it is now considered to be over-planted in many cities.  It is also considered to be invasive in some locations because of its profusion of seeds.  Other cities have banned the planting of this tree because its shallow root system cause sidewalks to lift and crack.  Many cultivars have been developed from this species, so there is a cultivar that will suit almost any site.  Some excellent cultivars to consider are:  'Cleveland', 'Columnar', 'Easy Street' Fact Sheet, 'Emerald Queen' Fact Sheet, and 'Parkway' Fact Sheet. 

Aesculus x carnea   Red Horsechestnut – is tolerant of drought, hot sites, low soil oxygen, salt spray on the tree surface, salt in the soil, and soil with a high pH.  Horsechestnut transplants easily bare root or B&B.  Height and width are 40 feet to 60 feet.  Leaves are dark green in summer, yellow or brown in autumn.  The red horsechestnut is one of the most popular trees in England, but it is actually hard to find in U.S. nurseries.  There are a few cultivars that will make excellent urban trees.  These include: 'Briotii' Fact Sheet and 'Fort McNair' Fact Sheet.  The white double flowering 'Baumann' Horsechestnut is very popular especially in older cities. Fact Sheet

Cladrastis kentukea  American Yellowwood – is tolerant of drought, pests, diseases, salt spray on the tree surface, and soil with a high pH.  Yellowwood transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height is 30 feet to 50 feet and wider than this.  Leaves are yellow in spring, bright green in summer, and golden yellow in autumn.  The 12 inch long panicles of white fragrant flowers in late spring highlight the value of this tree.  Yellowwood's name comes from the bright yellow heartwood of freshly cut lumber.  Fact Sheet   An excellent cultivar to consider is: 'Rosea' also called 'Perkins Pink', but it may be difficult to find.  Fact Sheet

Crataegus spp.  Hawthorn – is tolerant of drought, hot sites, compacted urban soil, low soil oxygen, salt in the soil, and soil with a high pH.  Hawthorn does have problems with diseases and pests, and it transplants with some difficulty bare root or B&B but it is suitable for CU-Structural Soil™  installation.  Height and width are 20 feet to 25 feet.  Leaves are dark green in summer, orange in autumn.  Most hawthorns have thorns which limit their use in the landscape.  However the thornless cultivars make excellent street trees.  Their white flowers and persistent red fruits give the tree year-round interest.  The low habit makes this tree ideal for growing under the utility lines.  Some excellent cultivars to consider are: C. crus-galli 'Inermis' Fact Sheet  C. phaenopyrum 'Washington' Fact Sheet  and C. viridis 'Winter King' Fact Sheet 

Fraxinus spp. Ash – is tolerant of drought, hot sites, compacted urban soil, low soil oxygen, soil with a high pH, and salt spray on the tree surface.   This tree is not recommended for areas where the Emerald Ash Borer (EAB) has been or is expected to invade.  This tree is also susceptible to diseases and other insect pests.  Mancana Ash Fraxinus mandshurica 'Mancana' and its cultivars are the only ash known at this time to be tolerant to EAB.  They are difficult to find in nurseries.  Ash transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height and width are 50 feet to 80 feet.  Leaves are dark green in summer, yellow to purple in autumn.  In the right location this very popular tree is ideal for the urban environment.  An excellent cultivar of White Ash F. americana to consider is 'Autumn Purple' Fact Sheet.  Some excellent cultivars of Green Ash F. pennsylvanica to consider are: 'Patmore' Fact Sheet and 'Urbanite' Fact Sheet, 'Marshall' and 'Summit'. 

Ginkgo biloba  Ginkgo – is tolerant of drought, hot sites, compacted urban soil, low soil oxygen, salt spray on the tree surface, pests, diseases, salt in the soil, and soil with a high pH.  Ginkgo transplants easily B&B but 
not bare root.  It is suitable for CU-Structural Soil™ installation.   It grows to a height of 50 feet to 80 feet and width of 30 feet to 40 feet.  Leaves are bright green in summer, a vivid yellow in the autumn which is second to none in brilliance, even in the south.  Ginkgo or maidenhair tree thrives in a wide range of soils and is tolerant of urban stresses.  Only fruitless male cultivars should be selected.  Ginkgo is resistant to storm damage and casts a light shade due to the narrow crown.  Some excellent cultivars to consider are: 'Magyar' Fact Sheet  'Presidential Gold®' Fact Sheet and 'Princeton Sentry®' Fact Sheet     

Gleditsia triacanthos inermis  Thornless Honeylocust – is tolerant of drought, hot sites, compacted urban soil, low soil oxygen, salt spray on the tree surface, salt in the soil, and soil with a high pH.  Honeylocust transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height and width vary greatly depending on the cultivar.  The range is 30 feet to 100 feet high and wide.  Leaves are bright green in summer, yellow in autumn.  Thornless honeylocust is an excellent fast growing street tree with essentially no seed pods.  Many arborists and landscape architects consider this to be one of the best urban trees available.  Honeylocust is also one of the last trees to leaf out in springtime and one of the first to lose its leaves in autumn, it is also one of the few trees well-suited for growing a lawn beneath it.  The tiny leaflets turn golden yellow in autumn before dropping and are so small they easily vanish into the grass below, without any raking being necessary.  Unfortunately, because this tree is so well suited for urban spaces, the honeylocust is over-planted in many areas.  Pests and diseases could become a problem in the future especially because of the over-planting.  Some excellent cultivars to consider are: 'Moraine', Shademaster®' Fact Sheet and 'Skyline®' Fact Sheet 

Juniperus virginiana  Eastern Red Cedar – is tolerant of drought, hot sites, low soil oxygen, salt spray on the tree surface, and salt in the soil.  Eastern red cedar transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  It grows 40 feet to 50 feet tall and 8 feet to 20 feet wide.  The leaves are medium green year round.  This conical evergreen is an excellent tree for mass plantings as well as providing windbreaks and tall hedges.  It is underused as a street tree.  Some excellent cultivars to consider are:  'Hillspire' Fact Sheet and 'Princeton Sentry'.

Koelreuteria paniculata  Goldenraintree – is tolerant of drought, hot sites, salt spray on the tree surface, diseases, salt in the soil, and soil with a high pH.  Goldenraintree transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  Height and width are 30 feet to 40 feet.  Leaves are purplish red in spring, bright green in summer, and yellow in autumn.  The goldenraintree tree provides an excellent source of yellow flowers in mid-summer.  The tree develops large clusters of seed pods in autumn that are somewhat persistent into the winter.  In most city locations the seed is not a concern, although in locations were the seeds can germinate, the tree might be considered a pest.  Fact Sheet   An excellent cultivar to consider is 'Summerburst®'.  Fact Sheet

Liquidambar styraciflua  Sweetgum – is tolerant of drought, hot sites, low soil oxygen, pests, diseases, and salt spray on the tree surface.  Sweetgum transplants by B&B only.  Because of the transplanting difficulty, it is not often recommended for urban planting.  Sweetgum can grow 35 feet to 85 feet tall and 15 feet to 40 feet wide depending on its location, climate, and amount of root space available.  The leaves are glossy green in summer and turn yellow, purple, orange, and red tones in autumn.  Sweetgum is an excellent tree for parks and lawns, but needs a large area for root development.  The fruit litter may be considered objectionable in some locations.  Some excellent cultivars to consider are:  'Moraine' and 'Slender Silhouette' Fact Sheet.  'Rotundiloba'  Fact Sheet is a cultivar that is seedless.

Nyssa sylvatica  Black Tupelo, Sour Gum – is tolerant of drought, compacted urban soil, air pollution, low soil oxygen, diseases, and salt spray on the tree surface.  Tupelo can be difficult to transplant, because of a tap root, so small sizes B&B and containerized trees are recommended.  It is best to move tupelo's in the early spring, before the leaves emerge.  The tree can grow 30 feet to 50 feet high and 20 feet to 30 feet wide.  Leaves are dark green in summer, yellow in autumn.  This native tree is noted for its consistent growth habit and beautiful autumn color.  An excellent cultivar to consider is: 'Red Rage' Fact Sheet
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Ostrya virginiana  Hophornbeam (Ironwood) – is tolerant of drought, low soil oxygen, pests, salt spray on the tree surface, and soil with a high pH.  Transplant Hophornbeam B&B or bare root in early spring.  Expect the tree to take a year or two to become established after transplanting.  This tree will grow 25 feet to 40 feet high and 18 feet to 30 feet wide.  Leaves are dark green in summer and change to yellow in autumn.  This tree does very well in urban plantings and on tree lawns, once it is established and begins to make excellent growth.  Unfortunately, this tree may be very hard to find in nurseries.  Fact Sheet   There is one new cultivar suitable for urban landscapes called 'Autumn Treasure™'.  Fact Sheet

Platanus x acerifolia   London Planetree – is tolerant of drought, hot sites, compacted urban soil, low soil oxygen, salt spray on the tree surface, and soil with a high pH.  London Planetree transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.  This tree will grow to a height of 70 feet to 100 feet and spread 65 feet to 80 feet wide.  Leaves are a dull dark green in summer and yellowish brown in autumn.  When this tree was first introduced, it became very popular and as it became over-planted, it started to develop disease issues.  However, many of the new cultivars are more disease resistant than the original hybrid and this is helping to make the tree suitable for installing in the city.  The olive-green to creamy exfoliating bark is the best asset of this tree.  It is very popular in open areas of parks and golf courses but should not be used along streets unless there is plenty of room for this large tree to grow.  Some excellent cultivars to consider are:  Exclamation' Fact Sheet, 'Columbia' and 'Yarwood'.

Quercus phellos   Willow Oak – is tolerant of drought, hot sites, low soil oxygen, pests, diseases, salt spray on the tree surface, and salt in the soil.  Willow Oak transplants easily B&B because of its fibrous root system.  It will grow to 40 feet to 60 feet high and spread to 30 feet to 40 feet wide.  Leaves are bright green in spring and summer, then change to yellow-brown and russet-red in autumn.  This tree is the best oak for its form and beauty and dealing with the urban environment.  It makes an excellent street tree for locations where there is plenty of room for this large tree to grow. Fact Sheet   There are no well-known cultivars.

Quercus robur  English Oak – is tolerant of hot sites, air pollution, salt spray on the tree surface, salt in the soil, and soil with a high pH.  English Oak transplants with some difficulty bare root so B&B is the preferred means of transplanting.  This oak is suitable for use in CU-Structural Soil™ installation.  English Oak has a height and width of 40 feet to 60 feet.  In some landscapes this tree can grow to 100 feet tall and wide.  The leaves are dark green in summer but will have no color in autumn.  This oak can grow to become a very large and beautiful tree.  English oaks have been known to live for over 300 years.  It is very popular in Europe and gaining popularity in the U.S.  English Oak has become a favorite tree for hybridizers as they develop new cultivars for our cities of the future.  Some excellent cultivars to consider are: 'Crimson Spire™'  Fact Sheet,  'Skymaster®' Fact Sheet and 'Skyrocket®' Fact Sheet

Quercus rubra  Red Oak – is tolerant of drought, hot sites, compacted urban soil, air pollution, salt spray on the tree surface, salt in the soil and soil with a high pH.  Red Oak transplants with some difficulty bare root so B&B is the preferred means of transplanting.  Red Oak has a height and width of 60 feet to 75 feet although it has been known to grow to 100 feet.  The leaves are pink to red in early spring and turn to dark green in summer.  In autumn, the Red oak will usually turn a beautiful russet red to bright red.  Red oak will adapt to acid or alkaline soil and is suitable for parks, golf courses, and wherever adequate growing space is available. This beautiful but huge tree should only be planted with plenty of space.  Fact Sheet   There are no well-known cultivars.

Taxodium distichum  Baldcypress – is tolerant of drought, compacted urban soil, low soil oxygen, salt spray on the tree surface, pests, diseases, and salt in the soil.  Baldcypress transplants with difficulty bare root and B&B so expect the tree to take some time to recover after transplanting.  This tree will grow to a height of 50 feet to 70 feet and a spread of 20 feet to 40 feet.  The needles are bright yellow in spring and darken in summer to medium green.  In the autumn they become russet to orange-brown.  Although baldcypress is native to wetlands along running streams, growth is often faster on moist, well-drained soil.  It is a tall tree that has excellent possibilities as a street tree.  Fact Sheet   An excellent cultivar to consider is: 'Shawnee Brave®'  Fact Sheet.  Due to transplanting problems, young trees are the best option for purchase.

Tilia cordata  Littleleaf Linden – is tolerant of drought, hot sites, compacted urban soil, air pollution, salt spray on the tree surface, and soil with a high pH.  The Littleleaf Linden transplants easily bare root or B&B and it is suitable for CU-Structural Soil™ installation.  Height and width are 50 feet to 70 feet.  Leaves are dark green in summer and yellow in autumn.  Littleleaf linden is selected for its vigor and improved branching habit.  It is a good specimen tree and suitable for areas where adequate root space is available.  Arborists and landscape architects enjoy using this tree due to its predictably symmetrical shape.  Littleleaf linden is a prolific bloomer.  The small, fragrant flowers appear in late June and into July.  Many bees are attracted to the flowers, and the dried flowers persist on the tree for some time.  Some excellent cultivars to consider are: 'Shamrock®' Fact Sheet and Chancellor®.  'Greenspire linden' is not recommended because of the leaves producing a dense shade that kills any groundcovers and grass around the tree. It also produces a proliferation of acute branch angles and many branches that break off in wind and winter and litter the ground under this tree.

Ulmus americana Princeton Elm – was originally selected in 1922 by William Flemer for its dense symmetrical upright form and dark green foliage, it has since proven to be one of the best American Elms for resisting Dutch Elm Disease. It is tolerant of drought, hot sites, compacted urban soil, salt spray on the tree surface, diseases, and soil with a high pH.  It transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation. Zone: 4 Height: 65’ Spread: 50’ Shape: Upright vase Foliage: Dark green Fall Color: Yellow  Dutch elm disease resistance. Fact Sheet  
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Ulmus parvifolia  Lacebark Elm – is tolerant of drought, hot sites, compacted urban soil, salt spray on the tree surface, diseases, and soil with a high pH.  It transplants easily bare root or B&B and is suitable for CU-Structural Soil™ installation.   The average height and width are 40 feet to 50 feet.  Leaves are dark green in summer and yellow in autumn.  This beautiful elm not only has attractive bark, it also has dark green leaves that turn yellowish red or purple in autumn.  This magnificent elm can grow up to 70 feet high and wide, so it needs a lot of space when making the decision about where to install it.  Many arborists and landscape architects consider this tree to be one of the most beautiful shade trees for the future.  Some excellent cultivars to consider are: 'Allee®' Fact Sheet, 'Athena®' and 'Bosque®'.

Sources  
  • Alvey, Alexis, “Trees Tolerant of High Soil pH”, Cornell Cooperative Extension of Suffolk County, 2011.
  • Appleton, Bonnie, et. al. “Trees for Hot Sites”, Virginia Cooperative Extension, Virginia Tech, May 1, 2009.
  • Appleton, Bonnie, et. al. “Trees for Problem Landscape Sites - Air Pollution”, Virginia Cooperative Extension, 2009.
  • Bomberger, Kim, “Preferred Trees for Kansas”, Kansas State University, 2005.
  • Clatterbuck, Wayne K., “Tree Susceptibility to Salt Damage”, Agricultural Extension Service, The University of Tennessee, 2003.
  • Coder, Kim, “Flood Damage to Trees”, Warnell School of Forest Resources, 1994.
  • Cornell Fact Sheets, "Tree Root Damage", 2011.
  • Evans, Erv, “Drought Tolerant Trees”, North Carolina State University, 2000.
  • Hansen, Mary Ann, “Problem-free Trees for Virginia Landscapes”, Department of Plant Pathology, Virginia Tech, 2006.
  • Harris, R.W., "Arboriculture: Integrated Management of Landscape Trees, Shrubs and Vines", Prentice Hall, Englewood Cliffs, NJ. 1992.
  • J. Frank Schmidt & Son Co.  - Fact Sheets
  • Macie, Ed, "Trees for Energy Conservation Home", USDA Forest Service, March 2013.
  • Mann, Gordon, “Trees during a Drought”, Archive #39 from Online Seminars for Municipal Arborists, July/August 2011.
  • Rogers Trees and Shrubs, “Trees that Tolerate Urban Soil”, Rogers Plants, Inc. 2012.
  • Strother, Ellen, “Tree Species Guide”, Clemson Institute for Economic & Community Development, no date.
  • Sulistijorini; et. al. “Tolerance Levels of Roadside Trees to Air Pollutants Based on Relative Growth Rate and Air Pollution”, Bogor Agricultural University, Indonesia, 2011.
  • University of Minnesota Extension Service, "Protecting Trees & Shrubs Against Winter Damage", Advocate, Winter 2004.
  • University of Minnesota, “Trees and Shrubs: Diseases, Insects and Other Problems”, Sustainable Urban Landscape Information Series, 2006.
  • Ware, George H., “Selecting Trees for Clay Soils”, The Morton Arboretum, 1980.


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