Protecting Trees and Shrubs From Road Salt Spray

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Salt spray damage to pines. This can be avoided by planting salt-resistant plants in from of them to trap the spray. Source: cdn.greenhousemegastore.com

With this extra-cold winter, even gardens in warmer parts of North America are facing road salt spray damage. This is caused by very fine droplets of salty water given off by vehicles driving along a road treated with deicing products. The faster the vehicles drive in the sector, the further the salt spray penetrates onto neighboring properties.

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Witch’s brooms caused by salt spray damage are common on trees growing near roads treated with de-icing salt. Source: infamousginger.wordpress.com

This kind of spray does not necessarily contaminate the soil (that kind of damage mostly occurs within a foot or so of the road, where particles of rock salt are deposed and that’s a different story entirely), but instead harms plants well back from the road, sometimes up to 30 feet (9 m). Damage includes reddened, dying needles on conifers, burned or scorched leaves on broadleaf evergreens and bud death and twig dieback on deciduous trees and shrubs, followed by witches-bloom growths in the summer when the plant tries to recuperate.

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Wrapping didn’t protect these arborvitae (Thuya occidentalis) from damage: the salt spray soaked through and burned the foliage on the side nearest to the road. Source: sk.extension.org

Many hard-working gardeners bundle up susceptible trees and shrubs with burlap or other winter protection products to catch the spray. However not only is this a lot of work, but it becomes nearly impossible to continue to carry out as the plants increase in size, especially trees. Besides, wrapping is only effective if salt spray is very light. Where it is heavy, it will soak through the covering and kill the needles and buds just underneath.

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Salt spray readily condenses on shrubs with multiple branches or thorns like this rugosa rose (Rosa rugosa), also known, very aptly, as salt spray rose. Source: florafinder.org

To avoid such damage, plant shrubs and trees that are resistant to salt spray between the road and sensitive plants so they can act as a filter. Especially consider species with abundant twigs or branches, as such as rugosa rose (Rosa rugosa), Siberian peashrub (Caragana arborescens), and shrubby cinquefoil (Potentilla fruticosa), as the salt will condense even more readily on the branches of these resistant plants, thus better protecting the plantings in the background.

Or simply avoid planting sensitive woody plants anywhere near a busy road and use deciduous perennials instead. Since these plants lose their aerial parts in the fall, leaving no living stems or leaves on which salt spray can condense, they are indifferent to this kind of damage.20180120A cdn.greenhousemegastore.com

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