Windbreaks that tolerate road salt spray drift

Windbreaks and farm woodlots that are located along major highways and rural roads can be damaged or killed-off by salt spray from winter applications of road salt on highways. Passing cars and trucks lift water and road salt residue into a fine mist that can travel with wind into adjacent farm fields and coat trees. Major four-lane highways are worse for producing drifting salt than smaller highways or rural roads due to faster vehicle speeds and frequent large trucks that create larger amounts of salted mist.

Many species of trees and shrubs that are often used for windbreaks are susceptible to desiccation injury by drifting road salt spray. Research shows that susceptible tree and shrub species are more easily damaged by road salt near the end of winter than exposure to salt spray in early or mid-winter. As trees overcome winter dormancy and prepare for spring growth, they become more susceptible to the affects of road salt residue.

Figure 1. A farm windbreak of blue spruce along a highway is tolerant to road salt spray drift. Good growth, healthy dark green or greenish-blue foliage and no needle browning indicates no salt injury is occurring.

Orchard trees, such as peaches, apricots, plums and apples are also easily damaged by drifting road salt spray along highways. Pears are somewhat less sensitive to road salt drift from highways. Commercial fruit orchards located downwind of highways have been damaged previously by winter road salt where studies have found high concentrations of sodium chloride on fruit wood and on dormant buds more than 100 meters downwind of highway properties.

Research surveys previously conducted by the University of Guelph, Horticulture Sciences have identified a number of tree and shrub species that can tolerate the effects of road salt along highways. Farm properties located along highways will have healthier windbreaks if they select trees and shrubs that are known to have tolerance to salt. Landowners can avoid species that have been identified as susceptible to road salt injury.

Figure 2. Eastern white cedar is susceptible to road salt injury downwind of highways. Lower branches are dead or dying off from several winters of salt spray. Green foliage at the tops of trees indicates where salt spray concentration declines and suggests that large mature hardwoods or large conifers would be less affected by road salt drift where the main canopy has grown above most drifting salt spray.

Fruit orchards located along highways can be protected by windbreaks consisting of trees that are tolerant to road salt, to catch and reduce the amount of road salt that is in the air before it enters the orchard. Some orchard producers have had good results where Colorado blue spruce and Austrian pine have been planted in mixed windbreaks adjacent to highways. Along highways, eastern white cedar and white spruce are not tolerant to road salt and often die back or show foliage burning as a result of road salt spray.

Figure 3. Conifers blue spruce, Austrian pine and Norway spruce are more tolerant to drifting road salt mist along highways during winter and can help protect sensitive orchards by catching road salt spray before it enters the orchard.

Healthy conifer windbreaks also help to catch drifting fungicide and insecticide spray material that may come from orchards, vineyards, small fruit or vegetable fields during spring and summer. The trees also create a visual barrier to passing motorists and can reduce noise significantly from orchard airblast sprayers and other noisy jobs.

To keep windbreaks functioning properly, it is important to renovate ineffective old windbreaks that are missing lower branches or windbreaks full of holes due to missing trees. Trees are entirely renewable.

The following is a list of tree and shrub species that have been observed in research surveys that tolerate road salt spray (ref. G. Lumis, University of Guelph). These species can be used on farms located along highways and rural roads where windbreaks are desired. A rating of 1 is most tolerant to road salt, while a 2 rating is mildly sensitive to road salt and is still useful along highways. The final grouping lists conifers that are very sensitive to damage by road salt spray drift and should not be planted along roads.

Tolerant conifers

Blue spruce, Picea pungens 1
Jack pine, Pinus banksiana 1
Mugho pine, Pinus mugo 1
Austrian pine, Pinus nigra 1
Red cedar, Juniperus virginiana 1
Juniper, Juniperus sp. 2
Norway spruce, Picea abies 2

Tolerant deciduous trees

Norway maple, Acer platanoides 1
Horse-chestnut, Aesculus hippocastanum 1
Tree of Heaven, Ailanthus altissima 1
Honey locust, Gleditsia triacanthos 1
Cottonwood, Populus deltoides 1
Black locust, Robinia pseudoacacia 1
Shagbark hickory, Carya ovata 2
Russian-olive, Elaeagnus angustifolia 2
White ash, Fraxinus americana 2
Largetooth aspen, Populus grandidentata 2
Lombardy poplar, Populus nigra 2
Trembling aspen, Populus tremuloides 2
Choke cherry, Prunus virginiana 2
Pear, Pyrus sp. 2
Red oak, Quercus rubra 2
European mountain ash, Sorbus aucuparia 2

Conifers very sensitive to road salt

(do not plant near salted winter roads)

Yew, Taxus sp.
White spruce, Picea glauca
Red pine, Pinus resinosa
Scots pine, Pinus sylvestris
Eastern white cedar, Thuja occidentalis
White pine, Pinus strobus
Eastern hemlock, Tsuga canadensis

Tolerant deciduous shrubs

Siberian peashrub, Caragana arborescens 1
Sea-buckthorn, Hippophae rhamnoides 1
Staghorn sumac, Rhus typhina 2
Burningbush, Euonymus atropurpureus 2
Honeysuckle, Lonicera sp. 2
Japanese lilac, Syringa amurensis japonica 2