During the winter months I spend a lot of time traveling the backroads of the North Country looking for logs. Consequently, I also look at zillions of roadside trees and lately two species have unfortunately caught my eye: the Hemlock and White Pine. Both, but especially the Hemlock, are showing severe browning of their needles. The affected trees are almost always on the lower side of roads and it seems logical that this severe damage has been caused by salt.
I phoned for some information from the soil conservation department and my suspicions were confirmed. Salt pollution of soil along highways is greatest at the end of winter. Saline water retards growth and causes "foliar" browning, death of flower buds, twig dieback, or outright death.
Species that are most prone to damage include Sugar Maple, Balsam Fir, Beech, Red and White Pine, and Eastern Hemlock. Those with high tolerance include Horse-Chestnut, Red and White Oak, Black and Honey Locust, and Staghorn Sumac. The birches, other maples, Aspen, Cherry, Basswood, Hickory, and Elms fall some- where in between.
Whereas the Hemlocks and Pine show browning during the same winter, it is obviously later that you notice damage in the hardwoods. They may show light green or yellow foliage, marginal scorch on leaves, and twig dieback. The Sugar Maples assume fall colors early and leaves are shed earlier than those of healthy Maples.
If you are planning to plant a tree along town or state roads, do research on your specie selection. If you have a favorite tree that is being affected by salt, here are a few things you can do:
1. Alter the drainage pattern away from the tree
2. Rake in 1 lb. of gypsum per 100 sq. ft. under the tree and out to 10' beyond the dripline. (The gypsum replaces the harmful salts with calcium.)
3. Water as soon as frost leaves the ground to leach out the salt
4. Have soil tested, fertilize accordingly, and add lime if pH is too low.