URBANA, Ill. — Salt causes damage to plants in yards and along driveways in several ways, said University of Illinois Extension horticulture educator David Robson.
Use of salt on highways, sidewalks and driveways has increased over the years with greater emphasis on safety. So has the damage to plants.
Symptoms
Salt injury symptoms resemble drought or scorch stress. Foliage can yellow and appear stunted. Leaf margins turn brown and curl.
Some leaves may exhibit fall colors in July and August. Most damage starts in early April through May as new growth starts.
Evergreens, however, react quickly and severely to salt injury. The needles will turn yellow and brown from the tip down in the early spring.
An easy diagnostic tool is the location of injury. Most plants will suffer leaf or needle damage on the side of the plant facing the road, sidewalk or driveway.
Salt damage
According to Robson, salt attracts moisture. Rock salt does the same in soils.
High amounts of salt in the soil can give the appearance of drought conditions as the salt sucks up all the water from the soil and even pulls it from the plant roots.
When the salt dissolves, the sodium and chloride molecules separate. The roots, leaf margins and growing tips easily absorb chloride ions. Scorch-like conditions develop.
Sodium ions prevent the soil from clumping. The result is heavily compacted soil that can’t breathe or allow water movement. Roots can’t function and may rot.
Excessive salt can tie up key nutrients such as magnesium and potassium, two of the important elements in chlorophyll production.
Limit use of salt
The best way to reduce salt injury is to limit the amount of salt used for de-icing. But this might not be practical in terms of human and vehicular safety, Robson said.
Calcium chloride is a safer alternative for plants, though the cost in terms of equipment, anti-caking agents and purchasing is prohibitive to most communities.
It might be a good source for homeowners with a few feet of sidewalk and driveway.
Sand, small gravel and cinders provide adequate traction for cars and trucks, but have little effect in melting snow or ice.
Urea fertilizer (45-0-0) can also be used to melt ice and snow, but excessive fertilizer can also cause damage to plant roots and leaves.
Most damage to plants occurs from late-season applications of salt, Robson noted. Avoid using salt after March 1.
Avoid piling salt-containing snow around plants. If unavoidable, flood or irrigate the area heavily in spring to dilute the salt buildup around roots.
However, too much water can cause as many problems as too much salt.
Robson noted some plants are more tolerant of salt and can be used in areas where salt buildup is possible.
High tolerance
Salt-tolerant plants include Norway maple, horse chestnut, birches, honeysuckle, spruces, poplars and aspens, white and red oak, Russian olive and Vanhoutte’s spirea.
Low tolerance
Low-tolerant plants include red and sugar maple, alders, most pines and firs, burning bush, dogwoods, lindens, yews and viburnums.
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