By Ken Johnson
Now that the temperatures have started getting colder, and we’ve had our first snow fall, many of us may be getting ready to get the salt out and ready for use. While salt is great for melting ice and keeping driveways and sidewalks clear of ice, it’s not so great for many of our plants.
The most commonly used salt for deicing purposes is rock salt (sodium chloride). When the salt is dissolved into water its ions, sodium and chloride, will separate. These ions are what cause the damage to plants.
Plants can be affected by salt in two different ways. Salt that is sprayed onto plants, for example when a car drives by, can damage cells and plant tissues that are sensitive to chloride ions. The ions will enter into the plant and accumulate in the growing tips to toxic levels. This most commonly occurs on the sides of the trees facing the road and plants that are downwind. Evergreen plants may develop pale green, yellow or brown foliage in late winter and early spring. Deciduous plants will often suffer from killed buds and twig tips which can lead to dense clusters of twigs forming, called witches’ broom. Flowering plants may not bloom. Often times plants will grow out of the damage if it is not to extensive.
Salt in the soil will affect plants differently than salt sprayed onto them. When there are high levels of salt in the soil, nutrient uptake can be reduced. It will also cause the soil particles to hold water tighter, making less water available to plants. Additionally, salt can affect the structure of the soil. High amounts of sodium in the soil may prevent the soil from clumping. This will make the soil susceptible to compaction. When plants take up sodium and chloride ions they can build up in the growing points of the plants and become toxic. This can lead to stunted yellow foliage, leaf scorch, twig dieback and stunted growth.
To limit or prevent salt damage to plants, use salt judiciously. Limit salt applications to high-risk locations such as steps, and walkways and driveways that are on an incline. Wait to apply salt until after you’ve finished shoveling and/or plowing. If possible try to wait until there is no longer a threat of snow. Doing this will help prevent the movement of salt into the landscape. Also, avoid using pure salt. Mix salt with an abrasive material such as sand, ash or kitty litter. While the abrasive material won’t melt the ice, it will help with traction. There are alternative deicing materials that can be used, that aren’t as damaging to plants as rock salt (they can still cause damage though), such as calcium chloride, magnesium chloride and calcium magnesium acetate. One of the drawbacks of these materials is that they are much more expensive than rock salt. University of Wisconsin Extension has an excellent fact sheet on salt and its effects on the landscape. It also lists the salt tolerance for many common wood landscape plants as well as alternative ice control products. It can be found at: http://learningstore.uwex.edu/assets/pdfs/A2970.pdf