If the tips of branches are brown, particularly those branches close to the ground, then this is a classic symptom of grit salt damage. But these symptoms are not always easy to detect. Water is drawn out of the plant and the leaves often turn brown, starting from their edges. Grit salt effectively over-fertilises the plant, giving it too many nutrients and removing water from it. The most vulnerable plants are conifers like thujas, as well as rhododendrons. If there is too much grit salt in the soil, they can have a particularly strong reaction.
If the hedge is already damaged, then the only way to help is with frequent, intensive watering. This will allow the layer of salt to penetrate deeper layers of soil so that it can no longer damage the hedge. This will only work if the ground is not frozen. Pour around 20 litres of water per square metre onto unfrozen ground every five days for approximately one month. If the hedge is unprotected during winter and has accumulated a layer of salt, then a thorough wash with the garden hose should help.
To prevent salt damage in the long term, trees and plants that are less sensitive to salt should be planted in areas facing the road. Some suitable plants include firethorn, alder buckthorn, burnet rose, snowberry, lilac and certain species of spiraea, viburnum and—among the conifers—blue spruce, Austrian pine and mountain pine.