Winter time, with all its joy and splendor, also brings a few headaches to Wisconsin gardeners. The snow and ice that falls on streets, sidewalks, and driveways requires management for safety reasons. Deicing compounds present challenges for landscape plants that might surround those structures. Most are not environmentally friendly and can easily mean the demise of existing plants.
The most common deicing compound used is salt, or sodium chloride, the same salt used on the kitchen table. According to the Wisconsin Department of Transportation, this state uses 526,000 tons of salt per season on roads, and this figure does not account for the additional amount used by homeowners and businesses.
Humans have been aware of the toxic effect of salt on plants since ancient times. Ancient armies used salt as a form of biological weapon by “salting” their enemy’s fields to destroy crops and make them inhospitable for future planting. Both components of salt—sodium and chloride—are toxic to plants in high concentrations. When salt dissolves in water, the sodium and chloride ions separate, and the sodium substitutes itself for the nutrients needed by the plants, making the other, required nutrients unavailable to the roots. Additionally, the roots absorb the chloride ions, transporting them to the leaves where they interfere with photosynthesis. More plant damage occurs if salt is applied in early spring/late winter when the plant is breaking dormancy and absorbing more water.
Salt damage does not limit itself to the root level. Moving traffic and wind causes salt spray to coat the leaves, buds, twigs, and branches of plants. This coating reduces the cold hardiness of the plants and increases the incidence of freeze damage.
While we certainly cannot stop deicing travel ways, we can take some measures to minimize damage to plants. When possible, use something other than sodium chloride. Other deicing products include calcium chloride, calcium magnesium acetate, potassium chloride, or magnesium chloride. However, these products are all significantly more expensive, costing up to ten times as much as sodium chloride.
In the alternative, use a deicing agent on only high-risk, critical areas. In other areas, use sand, kitty litter, cinders, or ash. When necessary, combine small amounts of salt with these materials. Apply whatever material you choose, including the deicing agents, only after all snow has been plowed or shoveled for maximum efficiency.
Cover plants sensitive to salt spray with burlap or place a barrier around them to protect them. Do not shovel salt-laden snow onto the root zone of plants.
In areas where salt use is necessary, plant salt-tolerant vegetation. Some plants can tolerate more salt than others, but even salt-tolerant plants will die with an overdose. UW-Extension has a publication available online entitled “Winter Salt Injury and Salt-Tolerant Landscaping Plants” that lists trees, shrubs, vines, ground covers, and herbaceous plants that are suitable for planting in areas that are more prone to salt use. Purdue Extension also has an excellent publication available online entitled, “Salt Damage in Landscape Plants.” This has a specific list of plants with graded sensitivity to the different methods of salt contamination.
In the event of heavy salt use, water the soil heavily (6 inches) at the soil level to flush out any residual salt. Rinse off the foliage during a warm spell, preferably before bud break.
With a little care, plants will make it through to another spring and beautiful growing season.
Certified Master Gardener