It is winter and many areas will be using salt on roadways, sidewalks and driveways. What effect does salt (NaCl) have on trees?
Salt (sodium chloride) applied as a deicing agent on streets and sidewalks causes severe damage to many species of roadside and lawn ornamentals. Damage results when salt passes into the root zone from snow; or when it comes in contact with foliage and branches in the form of spray created by passing cars. Often times salt laden snow is piled up on or near plants along the driveway or walkway. Plant sensitivity to salt varies greatly among species. Many ornamentals exhibit a very high degree of tolerance while others, particularly shallow-rooted species and evergreens, are readily injured.
Salt will damage plants by causing "burn" to the roots and foliage it comes in contact with. This results from the natural movement of water or sap from an area of high concentration within plant cells to one of lower concentration in the soil or on foliar surfaces (remember osmosis from high school?) Injury due to desiccation is particularly severe during dry periods.
WHAT CAN YOU DO?
In areas subject to deicing salts or natural salt spray, injury can be minimized by proper initial selection of planting stock. Right Tree... Right Place! In addition, calcium chloride is an effective deicing agent which is much less toxic to plants and should be substituted for sodium chloride on pavements around ornamentals whenever possible. Other materials including sand and urea are valid, but less effective, substitutes for sodium chloride. Diverting runoff from salted pavements away from existing plantings is the best way to prevent salt injury. Similarly, protective barriers of burlap, polyethylene, wood, etc. will help prevent salt spray from coming into contact with foliage and branches. If you can, try and keep the plowed salt laden snow away from the root zone of your plants.
Check with your landscaper or Arborist for a list of salt tolerant plants that can be used in susceptible areas. Here is an article from Penn State - extension.psu.edu/techniques-for-dealing-with-road-salt-injury