This is the time of year when Mankato City Forester Brian Hagberg is perusing landscaping catalogues and planning for next spring’s plantings.

When selecting what to grow in the city boulevards, Hagberg has to choose plants that can withstand the harsh conditions in that small strip of earth between asphalt street and concrete sidewalk: heat, limited space, a lack of moisture and, in the winter and spring, salt.

The deicing salt used on city streets can stunt the growth of trees and kill off sensitive plants. Homeowners may notice the symptoms — browning foliage, slow growth — in greenery bordering streets, sidewalks and driveways that are salted in the winter.

Even trees several yards off of a roadway can be sprayed with a salty slush by passing traffic.

Dean Pettis, horticulture specialist at Drummers Garden Center and Floral in Mankato, said there is no magic gardening product that will reverse salt damage. But homeowners can take action now, over the winter and in the spring to limit the effect.

George Rosati, director of public works, said about 1,400 tons of salt are used on Mankato city streets every winter, although that total varies from year to year. New technology and techniques for spreading the salt limit the damage it does to lawns, but there is no way to eliminate it, Rosati said.

Salt damage symptoms

Gary Johnson, a University of Minnesota Extension professor, said deicing salt damages plants in two main ways: what he calls “spray drift” and runoff.

Spray drift mostly effects vegetation along busy highways, but its symptoms are also visible on city streets. The spray drift is caused when salt mixes with slushy snow and is blown onto plants up to about 60 feet from the roadway.

When the salt mix coats the needles of evergreen trees and shrubs, it can cause an abnormal browning. Abnormal, Johnson said, because only the side of the evergreen facing the road is affected.

Spray drift will also coat the branches and buds of deciduous trees, causing a deformity known as “witches broom.” New growth sprouts in distinctive tufts around buds that have been killed by salt.

Worse than spray drift, though, is when salt mixes with snow runoff and gets into the soil.

“Runoff is actually more damaging in that it can kill plants,” Johnson said.

Salt in the soil makes it harder for plants to take in water, stunting their growth. Deciduous trees will often leaf out late and drop their leaves early.

Johnson said many people see the symptoms, but assume they are caused by something other than salt. Salt can cause scorched leaves, for example, which are also a symptom of drought or root damage.

Prevention

Pettis said it isn’t too late yet to give trees and plants a good soaking before the ground is frozen. The additional moisture will help plants withstand salt damage and other winter stresses.

He said another soaking in the spring will leach the salt out of soil in runoff areas.

One basic prevention against salt damage is to erect a barrier. Snow fencing can keep spray drift off of trees, and small trees and shrubs can be wrapped in burlap.

Avoiding the use of salt on sidewalks and driveways will also limit damage.

Johnson recommended deicing with calcium chloride or calcium magnesium acetate, alternatives to salt that are less harmful to vegetation. Still, they must be used in moderation.

“They’re not safe, but they’re safer,” he said.

A better solution may be to spread grit on sidewalks instead of salt. Pettis recommended sand or kitty litter.

If all else fails, think about transplanting next spring.

“Just move the plants out of harms way,” Johnson said.