As we've already experienced this year, winter in Illinois commonly means snow and ice. Though plowing and shoveling are the primary means of removing snow and ice where they aren't wanted, deicing salts also help prevent slick, hazardous conditions. While salt is great in its place, it's not so great for many things that may encounter it.
Rock salt (sodium chloride) is the most common deicer. It's cheap, effective, and plentiful but it does have some drawbacks. It is corrosive to both vehicles and concrete, and it can damage soil as well as plants. As rock salt dissolves in water, its ions (sodium and chloride) separate. These ions can cause damage in our landscapes in high enough concentrations.
High levels of sodium can damage the structure of soil, preventing it from clumping and making it susceptible to compaction, in turn reducing permeability and aeration. High sodium levels can also raise soil pH.
Nutrient imbalances can also be caused by high soil levels of sodium and chloride. These high levels can restrict plants' uptake of other essential nutrients leading to nutrient deficiencies. Chloride ions also can build up in the growing points of plants and become toxic, leading to stunted yellow foliage, leaf scorch, twig dieback, and stunted overall growth.
Just like the salt in your salt shaker, rock salt absorbs water. As it holds onto water, there is less available for plants. This can create drought-like conditions for plants, even when there is adequate soil moisture.
Salt spray, such as that spread by passing cars, also damages plants. Salt that lands on plant tissues can dry them out by pulling water out of plant cells. It can also enter the plant and accumulate in the growing tips to toxic levels. This most commonly occurs on the sides of trees facing a road and plants that are downwind. Many evergreen plants are very susceptible to salt damage, developing pale green, yellow, or brown foliage in late winter and early spring. Deciduous plants may suffer from killed or damaged buds and branch tips, which can lead to the formation of dense clusters of twigs, called witches' broom. Flowering plants may not bloom. If the damage is not extensive, plants may grow out of it.
So how can you help prevent salt damage to your soil and plants? There are various steps you can take:
- Use salt judiciously, especially after March 1. Once plants begin to break dormancy, they become even more susceptible to damage.
- Limit salt applications to high-risk locations like steps, along with walkways and driveways on an incline.
- Finish clearing snow before applying salt. This will help prevent the movement of salt into the landscape.
- Salt can also be applied before a storm arrives. This helps prevent ice from sticking to pavement, making removal easier and reducing the amount of salt required.
- Avoid using pure salt by mixing it with an abrasive material such as sand, ash, or kitty litter to help with traction.
- Use deicing materials that are less damaging to plants, such as calcium chloride, magnesium chloride, and calcium magnesium acetate. (These are more expensive than rock salt, however, and can still cause some plant damage.)
- Protect plants near the street with a temporary barrier, such as plastic or burlap.
- Hose off any plants that have experienced salt spray as soon as possible.
- As the ground thaws in spring, soils that have had a heavy salt load on them can be thoroughly watered to leach salt out of the root zone.
If you have areas in your landscape, such as near a road, which commonly has issues with salt damage you may want to look at plants that can tolerate higher levels of salt. There are several ways plants can protect themselves from salt. Some plants may have physical features that protect them from salt spray (these adaptations won't protect them from salt in the soil). This can include thick waxy surfaces, or tightly arranged bud scales. When it comes to salt in the soil, some plants can prevent salt from entering their cells or can simply withstand higher salt levels in the soil. It's important to note that even plants with some tolerance to salt can still be damaged by high levels it.
Some plants that have tolerance to both salt in the soil and spray include sweet gum, bald cypress, common horse-chestnut, red oak, juniper, eastern red-cedar, cranberry cotoneaster, potentilla, and rugosa roses. To see a more extensive list check out Winter Salt Injury and Salt-Tolerant Landscape Plants from University of Wisconsin-Extension.