As temperatures drop and snowfall increases this winter, Detroit’s road commissioners break out their plows and salt trucks in order to maintain safe roadways. 

However, the most common road salt used, sodium chloride, has been known by experts and road commissioners to cause damage to surrounding trees.

Dr. Bert Cregg, a Michigan State University Professor in the Department of Horticulture, says that excessive usage of this road salt can lead to tree death. 

Cregg says protecting trees from salt exposure and selecting salt-tolerant species are the first steps to mitigating this issue. 

Identifying salt damage in trees 

Cregg describes salt damage occurring in two ways: acute damage and chronic damage.

Acute damage refers to when tree trunks, branches, and leaves are exposed to salt. 

“If we think about the white coat of salt that accumulates on our cars this time of year, trees and shrubs adjacent to roadways are experiencing the same thing,” says Cregg

Acute damage is the easiest to identify.

In evergreen trees, such as Michigan White Pines, salt damage causes needle browning and can lead to tree death.

In deciduous trees, such as Oak and Maple trees, salt damage commonly causes “witch’s brooms,” which is when the ends of branches repeatedly die and grow back due to salt exposure, Cregg explains. 

Because chronic injury refers to damage that we can’t see as easily, it can be trickier to identify. Chronic injury occurs when road salt leaches into the surrounding soil and creates high concentrations of sodium and chloride.

Cregg says these high concentrations “reduce the plant’s ability to take up water from the soil solution, resulting in a form of drought stress.”

How to reduce salt damage on trees: protection and selection

Cregg suggests de-icing alternatives, such as beet juice or calcium magnesium acetate, which pose less environmental risk than typical road salt.

While the simple solution seems to be for road commissioners and residents to abandon their usage of road salt, this is an unrealistic approach considering sodium chloride continues to be the most affordable and efficient option for de-icing, and given Michigan’s harsh winters, public safety is often prioritized over environmental concerns. 

Due to this limitation, Cregg emphasizes the importance of creating physical barriers, such as placing burlap wrap or canvas screens around existing trees, to protect them from excessive salt exposure.

These physical barriers would help mitigate damage from the inevitable salt splash caused by cars on the roadway. 

When planting new trees around roadways, it’s important to consider that some tree species are more sensitive to salt exposure than others.

To aid this, Cregg advises homeowners and city planners to select salt-tolerant trees to ensure they can survive in the given environment. 

“Some salt-tolerant trees for our area include Bald Cypress, Kentucky Coffeetree, Japanese Tree Lilac, Dawn Redwood, Horse Chestnut, Hackberry, and Swamp White Oak.”

This story is a part of WDET’s ongoing series, the Detroit Tree Canopy Project.