The practice of salting the earth to destroy, at least symbolically, the product­ivity of a defeated enemy’s lands, has been in existence since ancient times. During a winter such as we have “enjoyed” this year, large amounts of salt have been used to clear streets and highways of snow and ice. Additional salt may have been used as a melting aid for driveways and sidewalks. While salt today does not have the kind of symbolism it did back then, it can still result in damage to landscape plants.
Salt causes damage to plants in two ways. Salt spray from roads may cause contact injury to leaves, buds and small twigs. Evergreens are particularly susceptible. With this type of injury, damage is usually more severe on the side of the plant closest to the source of the spray. Unless damage is very severe, plants usually recover from this type of injury.A more serious cause of damage is when melting salt alters soil chemistry. The most commonly used form of salt is sodium chloride. When this salt dissolves in water, it breaks down into sodium and chloride ions, both of which are toxic to plants if present in high concentrations in soil. Sodium blocks necessary nutrients such as potassium, calcium and magnesium from being available to plants. Chloride ions are absorbed by plants and accumulate in the leaves where they interfere with the production of chlorophyll and photosynthesis. If the salt does not break down, the water in soil becomes salt water resulting in damage to roots. Nobody recommends using seawater to irrigate plants.
In a normal Indiana winter, snowfall is often interspersed with periods of warmer weather and, frequently, rain. This helps prevent salt buildup in the soil and, when it does accumulate, can help to flush the salt out. This has not been the pattern this year. Much of the salt that has been sprayed out from the roads has remained in place. While spring may arrive with a great deal of rain, it may not.