Road salt is a key measure for making it through a Canadian winter safely. It is a big part of what keeps roads and sidewalks clear of winter snow and ice so we can travel easily even in the worst winter weather. However, road salt brings with it some unwanted side effects for our trees and shrubs.
We can see some of these effects during the winter itself, but most of the visible damage is obvious after the snow and salt have melted and spring has come.
Learn how to identify, treat, and prevent road salt damage to your trees so you can improve your tree health and extend its life!
Is Road Salt Harmful to Trees and Plants?
Road salt is most commonly sodium chloride, also known as rock salt or table salt. Calcium chloride, a salt from limestone, is also used as salt for roads and is slightly less damaging to plants than rock salt. However, this option is also more expensive.
Both types of road salt have always been known for their toxicity to plants. Because it is very effective at melting ice and making driving and walking safer in the winter, it is used across Canada regularly even though it poses risks to trees and plants.
When road salt is used around trees, the snow and ice mix with it to create a brine. This brine is absorbed into the nearby soil and then by the roots of trees and plants in the area. The tree’s vascular system pulls water up from the soil through its roots and pushes the excess out through tiny pores on the leaves. When the water moving through the tree is too salty, the salt collects on the edge of the leaves, causing damage there first that can easily spread, depending on how much brine the tree is absorbing through the soil.
Another way road salt can cause harm to trees is through airborne spray, such as when it is sprayed by a salting truck or passing cars. This spray hits the trees directly and can cause the leaves to die.
If you get to choose the de-icing materials that will be applied to areas near your trees and shrubs, choose one such as calcium magnesium acetate that is not as corrosive as road salt but still provides a similar de-icing effect.
What Does Salt Damage Look Like?
In the winter and spring, you may notice some road-facing trees look scorched on the side facing the road, and have full, healthy foliage on the opposite side. This is unfortunately a common sight around many large roads. As cars drive by, the tires create arcs of water that spray the road-facing side of the tree, covering these branches with salt that has melted into the snow, slush, and water. This damages the branches that get wet repeatedly all season, while the branches higher up or on the opposite side can stay unaffected.
Salt damage often looks like water stress on trees. Conifer trees like fir and pine turn their needles brown from the tip backwards towards the needle base. Broadleaf evergreen trees and deciduous trees develop brown leaf margins or kill the leaves entirely.
More severe salt damage on trees can lead to the death of branches, stunt the tree’s growth, destroy leaf and flower buds and in the most extreme conditions, kill whole trees.
How Can I Prevent Road Salt Damage On My Trees?
There are a number of ways you can protect trees on your property from damage caused by road salt in the winter.
- Plant salt-tolerant native species
- While many plants and trees native to southern Ontario are not naturally salt-resistant, some species are more tolerant than others. Red pine, red oak, ashes, birches and poplars are some native trees that are better choices to plant near roadways as they have a slightly higher salt tolerance than other native species.
- Water well
- If the temperatures during the winter drop and there is a brief thaw, it can be beneficial to water the soil around trees to help lower the concentration of salt near your tree’s roots. However, this should not be done while freezing or to low lying trees, as this can drown and freeze the roots in the winter.
- Wash the leaves
- Similarly, when temperatures go above freezing, you can wash the foliage off with water if your trees are in an area where airborne spray is hitting the leaves.
- Wrap the trees
- Wrapping your trees or shrubs in burlap can help protect the foliage from salt spray. Ensure you remove the wrap as soon as salting stops so your trees can benefit from the spring sunshine.
- Watch your snow placement
- If your trees are near a sidewalk or driveway that you have to shovel, try to place the shoveled snow away from the base of the trees. Leaving snow piles near your trees adds more salt to the soil in this area.
- Raise the grade
- If you are designing a landscape, avoid putting plants and trees at the bottom of slopes where there will be salty runoff in the winter. Raising the grade where plants and trees grow give them a better chance at absorbing better soil in the winter and spring.
- Choose alternatives to road salt
- Calcium magnesium acetate and coarse sand are all good alternatives to using road salt where possible. If you do require road salt, use as little as possible and minimize the throwing distance to reduce spray.
Can Damaged Trees Be Treated?
Luckily, if your trees are starting to exhibit signs of road salt damage, it can be reversed. In the spring after the snow has melted, water the soil around the trees as much as possible. This helps the salt to drain out of the soil more easily so your tree will absorb less of it as spring continues.
A certified arborist can also remediate the soil by drilling holes around the trees’ drip lines and replacing salty soil with organic matter. This helps to provide the trees with a salt-free area to grow and repair any existing damage.
If you are worried about the effect of road salt on your trees, P & A can help. Contact us to learn more about the options you have for protecting your valuable trees from road salt!