Here in Chicago and Cook County, when snow and ice coat our driveways and streets, we spread generous amounts of halite salt to melt the frozen precipitation and keep traffic moving. Indeed every Chicago mayor knows that if you fail to clear off the snow and ice, you will not be re-elected for another term.
However, while salt is wonderful for clearing snow and ice from the roads, it’s not quite so wonderful for our plants. According to Rutgers University Cooperative Extension, salt harms vegetation in a number of ways.
- Increasing water stress. In the root zone, water molecules are held very tightly by salt ions, making it difficult for roots to absorb sufficient quantities of water. In sensitive species, this “physiological drought” may result in depressed growth and yield.
- Affecting soil quality. The sodium ion component in rock salt becomes attached to soil particles and displaces soil elements such as potassium and phosphorus. As a result, soil density and compaction increases and drainage and aeration are reduced. In addition, chloride and calcium can mobilize heavy metals in affected soils. Plant growth and vigor are poor under these conditions.
- Affecting mineral nutrition. When the concentration of both the sodium and chloride components of salt in the root zone is excessive, plants preferentially absorb these ions instead of nutrients such as potassium and phosphorus. When this occurs, plants may suffer from potassium and phosphorus deficiency.
- Accumulating to toxic levels within plants. The chloride component of salt is absorbed by roots and foliage and becomes concentrated in actively growing tissue. Plants repeatedly exposed to salt over long periods of time may accumulate chloride ions to toxic levels, resulting in leaf burn and twig die-back.
There’s not a whole lot you can do about salt on town and city roadways. However, there are steps you can take to minimize salt contamination in your own yard. For starters, clear off the snow from your driveway with a shovel or plow first before applying ice-melting salt, and then use the minimal amount necessary to melt the ice and snow. Second, there are more environmentally friendly ice melting products that you can use instead of regular halite salt. Lastly, if your soil does become contaminated with salt, you can try adding plenty of water to dilute the salt. In some cases gypsum at 50 lb./1000 sq. ft. can be added into the top six inches of soil at the drip-line of trees. If the foliage of trees and shrubs becomes coated with salt, then wash it off with salt-free water. Try to plant trees and shrubs as far away as possible from streets, roads, and driveways to minimize salt contamination. If you must plant near the pavement, then plant salt tolerant plants.
This winter, let’s do all we can to prevent the as-salt on our soil and plants.