When salt dissolves, it decreases the freezing point of the water. Consequently, salt is often added to icy roads in wintertime. Afterwards, however, the salt can sometimes have detrimental effects on roadside plants.
Salty runoff from melting ice on roadways increases the salt content of the soil, altering its composition and potentially making it more easily compacted. Increases in salt concentration can decrease the rate at which plants can take up water from the soil; plants may also take up some of the excess sodium chloride in the place of the magnesium and potassium they also need, leading to nutritional deficiencies.
Plants suffering from high levels of soil salt concentration often resemble plants afflicted by drought or damage to their roots. Common symptoms include yellowed leaves with scorched edges; potassium deficiencies are a common problem. Needles on evergreen trees may turn yellow or brown in the spring.
Some species of plants can tolerate higher salinities than others. Colorado blue spruce and ponderosa pine, for example, are more salt-tolerant than red maple or sugar maple. Nonetheless, if you use salt to de-ice your road or driveway, it's best to use it in moderation and avoid overapplying salt if possible.