Plain rock salt is the most commonly used household and municipal ice melter for winter sidewalks and driveways. It occurs naturally. It is plentiful and cheap. The difficulty is that repeated applications of salt lead to a buildup of salt in the soil nearby. Unfortunately, concentrated salt from winter runoff is one of the most toxic environments for plants. To keep your landscape healthy, it is imperative to take precautions against the buildup that causes winter salt damage.
Winter salt damages plants in a few ways. Initially, salt infused road spray coats thin branch tips. In this way, salt makes a direct entry into plant tissue, diminishing cold hardiness and drawing out moisture. Next, the road is plowed and salt laden slush is pushed off of sidewalks and roadways, and into the landscape, including lawns and shrub areas. In the first phase of snow melt, salt drys roots in the same way as it dries branch tips, by simply attracting all the moisture to itself.
Later, as the water-saturated salt dissolves, its chemistry changes. The sodium and chloride ions are separated. Then the chloride ions are absorbed by roots, and from there they travel through the vascular tissue of the plant once it begins active growth. Scorched leaf margins and tip dieback are common problems in established shrubs. Young plants may be killed outright by toxic chloride levels. As for the sodium that was not absorbed, it remains to wreck the soil structure, making it difficult for moisture and gasses to move efficiently through the soil, thus impeding nutrient uptake.
Salt damage is seldom immediate. Rather, the damage progresses as salt levels build in the soil. Symptoms are easily confused with drought stress. Watch for such indicators as premature fall color, twig dieback, leaf margin scorch, browning of conifer needles or stunted growth.
The first and most obvious solution to this perennial risk is avoiding the use of salt. For homeowners, it may be as easy as changing your approach to dealing with winter ice. Maybe it’s not important that the thin layer of ice be melted if you can get traction. Spreading sand, kitty litter or sawdust are proven, effective ways to provide great traction over icy areas without polluting the soil. If the ice must go, nearly any other commercially available ice melter is less toxic to plants than sodium chloride, with the least toxic options often being advertised as “pet safe.”
Since homeowners have little control over the choice of road treatments used by highway crews, another approach is necessary for landscapes bordering municipally treated surfaces. The first rule here is to keep the ground well hydrated both ahead of and after winter. Heavy rain or irrigation can help to flush excess salt out of the root zone. Pay particular attention to plants as they begin to break dormancy, when they are especially sensitive to the effects of salt. Late applications of salt, after buds begin to break open, should be flushed off of branches as soon as it is safe and practical to do so.
When choosing plants for locations that will receive salt runoff, look for varieties that are resistant to its effects. Check with your local extension service for varieties that are best suited for your area.
Winter brings inherent challenges. It’s important to take safety seriously. With a little forethought, you can keep both people and plants safe when it’s time to weather that winter storm.
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