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Salt Spray From Roads
Salt (sodium chloride) is used by many communities to prevent ice on the streets. Unfortunately, salt spray from roads causes brown foliage on deciduous or evergreen trees and shrubs. It can cause "witches'-broom" on deciduous plants. A witches'-broom is a cluster of twigs that forms on a branch. Prolonged exposure to salt spray can lead to dieback. Salt spray can drift to plants from nearby roads as the tires of passing cars kick up a salty spray. The water evaporates, leaving a salt residue. Damage is usually greatest on the side facing a roadway, or in areas where the drainage pattern causes accumulation of de-icing salts. Although the salt is applied throughout the winter, most salt damage occurs in late winter and early spring when plants are beginning active growth.
The affected foliage may fall off in the spring, but usually the new spring growth may make the tree or shrub appear otherwise healthy. The trees or shrubs will unfortunately grow more slowly and remain stunted, and may eventually be killed by prolonged exposure. Salt accumulation in the soil can cause abnormal fall color, needle-tip burn and browning that starts on leaves’ edges and progresses toward their middle veins. There is little you can do to protect your trees from such a spray of salt coming from a road. If that cloud of spray appears, use copious amounts of water to rinse the foliage and branches of any affected plants when salt spray is heavy and then do it again in early spring. Do not do this if the temperatures are below freezing. Wait until they go above freezing. Another strategy to reduce salt damage to trees, is to plant trees as far from roadways as possible and select species that are tolerant of salt (see the charts on the left)
Dealing With Salt Accumulation
If you fear the soil around your trees has taken in too much road salt over the winter, flush the soil with water in the spring when it thaws. Apply 2" of water over a 2-3 hour period and repeat this task 3 days later. This will leach much of the salt from the soil and should send salts beyond the trees’ root zones, where they can’t harm the trees.
In any area that has been affected by salt accumulation in the past, it is wise to incorporate lots of organic material into any soil that is exposed to introduce new plants. Research has shown that adding gypsum along with the organic material will serve to reduce the damage of salts in that particular area in the future.
Salt On Sidewalks and Driveways
Salt can injure landscape plants when salt used on porches and sidewalks is shoveled or swept onto nearby shrubs, where it accumulates on the foliage or in the root zones. Most chemical deicers will have the same injurious effects, though calcium chloride is not as harmful as sodium chloride. Fertilizer is sometimes used, but it, too, can build up to toxic levels. Sand and ashes are not toxic but have the disadvantage of being easily tracked into the house. There are now on the market de-icing products that contain no salt and cause no harm to your trees. Go to Plant Safe Ice Melting Products