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University of Illinois Extension

Salt Injury to Plants

December 10, 2012

Salt causes damage to plants in your yard and along your driveway in several ways, said a University of Illinois Extension horticulture educator.

"Use of salt on highways, sidewalks, and driveways has increased over the years with greater emphasis on safety," said David Robson. "Unfortunately, so has the damage to plants.

"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 occurring in the early April through May period 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," he said. "Most plants will suffer leaf or needle damage on the side of the plant facing the road, sidewalk, or driveway. You can travel down some interstates and highways and notice the salt spray injury, which can travel several hundred yards."

How does salt damage the plants?

"First, salt attracts moisture," Robson explained. "Just pour water in a salt shaker and watch the salt clump. 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.

"Finally, excessive salt can tie up key nutrients such as magnesium and potassium, two of the important elements in chlorophyll production," he said.

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, however, 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.

"Kitty litter is sometimes used for traction. However, avoid the clumping types as these become quite messy," he said. "Kitty litter can be a problem when tracked indoors on shoes."

Urea fertilizer (45-0-0) can also be used to melt ice and snow. Remember that excessive fertilizer can also cause damage to plant roots and leaves.

"Most damage to plants occurs from late-season applications of salt," he 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 that some plants are more tolerant of salt and can be used in areas where salt buildup is possible. 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-tolerant plants include red and sugar maple, alders, most pines and firs, burning bush, dogwoods, lindens, yews, and viburnums.

"Healthy plants are able to withstand salt injury," Robson said. "Keep plants actively growing with a regular watering and fertilizing program. Prepare the soil properly for planting."

Source: David J. Robson, Extension Specialist, Pesticide Safety, drobson@illinois.edu

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