The harmful effects of rock salt and more on trees and plants
As you get ready for winter snows, think carefully about using de-icing chemicals such as salt.
The chemicals used to melt snow and ice help make walking safe, but they also can do serious harm to trees, shrubs and other plants near roads and sidewalks, according to Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle.
“Use these chemicals only when and where you really need them,” she said. “When you use them, do so sparingly.”
Salt damages plants mainly by drying out their tissues. “You’ll see it most often on evergreens, because they keep their leaves in the winter,” Janoski said. “The side of an evergreen hedge by the sidewalk often is brown by February or March, as a result of salt used on the walk.”
It’s not just plants near the sidewalk that suffer. When snow melts on salted streets, passing cars can throw a saltladen spray 20 or 30 feet away, damaging plants deep in front yards.
Some damage is harder to see. Salted spray that lands on the flower and leaf buds of deciduous trees can dry them out. “Those buds will never bloom,” Janoski said. Twigs and leaves growing from salt-soaked branches may be distorted or stunted.
When snow melts, salted water can soak into the soil, killing valuable microorganisms in the soil and drying out tree roots. In areas near walks and roads, salt can build up in the soil winter after winter. “Salt damage can slowly kill a tree over a period of years,” she said.
No plant is immune to salt damage, although some kinds of trees and shrubs are more tolerant than others, she said.
De-icing chemicals don’t just hurt plants. They also can corrode metal and damage the concrete of walks and patios and the wood of decks. If the chemicals are tracked indoors, they can damage carpet, wood and tile. Some chemicals leave an oily residue that is hard to remove.
Sodium chloride — rock salt — is the cheapest and most common ice-melting chemical. Other chemical cousins, such as calcium chloride, magnesium chloride, and potassium chloride, are also used. Potassium chloride is somewhat less damaging to plants, but “it’s not benign,” Janoski said.
Many products are a mixture of chemicals to work in a wider range of temperatures. “Read the directions on the bag and follow them carefully,” Janoski said. “Different products don’t all work the same.”
To minimize the damage, apply an ice-melting product only where it is necessary. “Use it on the areas of foot traffic where safety is paramount,” Janoski said. Consider using sand for traction where you can. “Sand is inert and won’t hurt your plants,” she said.
Don’t use salt or another chemical as a substitute for shoveling. Physically remove snow from the pavement first, and then decide whether you need to sprinkle a de-icer to keep ice from forming.
When you shovel snow from a place where salt or another chemical was previously applied, try to avoid piling it on the root zone of a tree or shrub or near evergreens to minimize the damage when the snow melts and the salty water soaks into the soil.
“People’s safety comes first, and these chemicals can have a role in making it safe to walk outdoors,” Janoski said. “But they aren’t harmless, so use them carefully, thoughtfully, and as little as possible.”