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Browning pine needles.

Salt damage on roadside pines.

Salt damage on plants

By Janna Beckerman

From eNews, January 12, 2006

Minnesota winters provide very little disease excitement for plant pathologists. Yes, there is the occasional ice storm, with broken limbs and branches, but for the most part, winter serves to numb a plant pathologist's brain, and he or she forgets the problems that are developing while plants are "sleeping." One such problem is salt damage.

Most people only think of salt damage and how it affects their cars. In Minnesota, 200,000 to 300,000 tons of de-icing salt is applied to roads each winter. Very few think about it what salt can do to plants.

How salt damages plants Salt, which is made up of sodium and chloride, becomes toxic to plants when it dissolves in water and the sodium and chloride ions separate. The sodium ions take the place of the much-needed phosphorus and potassium in the soil, making these two nutrients unavailable to the plant. Chloride ions are absorbed by the roots and transported to the leaves, where they accumulate and interfere with photosynthesis or chlorophyll production.

Have you ever tried to get table salt out of a wet shaker? Then you know salt absorbs water. Rock salt does the exact thing in the soil, absorbing the water that would normally be available to roots, causing root dehydration, a change in root physiology, and additional plant stress. Salt also damages plant cells, including buds and small twigs, thereby reducing cold hardiness and leaving tissue more susceptible to freezing damage.

You will most likely notice salt damage on the side of the plant that faces the road or a sidewalk, and the closer the plant, the more severely it will likely be affected. Usually, evergreen damage appears in late winter, with pine needles browning at the tips. Snow-covered branches are less affected by salt spray. It is more difficult to diagnose salt-spray damage on deciduous plants. Usually, leaf buds facing the road are killed or are very slow to break. Flower buds facing the road often fail to bloom. Repeated salt damage may result in shrub flowers having a witch's broom or tufted appearance.

How to prevent salt damage The easiest way to prevent salt damage is to avoid de-icing salts and use coarse sand to provide traction and make sidewalks and driveways less slick. If you must use salt, use it judiciously and erect barriers with plastic fencing or burlap or snow fencing to protect sensitive plants and minimize contact with salt. When possible, use de-icing agents with calcium chloride or calcium magnesium acetate, a salt-free melting agent made from limestone and acetic acid.

If an area is heavily salted, consider planting salt-tolerant plants like the ginkgo, winged euonymus, or Japanese tree lilac. Rugosa roses can take salt as well as the strongest margarita, and they can be seen growing next to the Atlantic Ocean. There are also numerous salt-tolerant cultivars with an array of color and fragrance: perennials like statice, sea thrift, and reed grass.

For more information on diagnosing plant damage--by salt or anything else--see the Extension diagnostics. Janna Beckerman is a plant pathologist with the University of Minnesota Extension Service.