by Anne Harrington PhD
Trees for Watertown
Rock salt is the No. 1 de-icer in the United States. It’s cheap, effective at melting snow and ice, and provides good traction on treated surfaces. But road salt is referred to as a “silent killer” because of the seen and unseen damage that it causes to infrastructure and the natural environment.
Tons of rock salt are applied every winter in the U.S. Nearly half a million tons are used annually for winter road maintenance in Massachusetts alone (Source: EPA, Nov 2020). That doesn’t include the amounts applied to sidewalks, parking lots, and private property. Rock salt is cheap, effective at melting snow and ice, and provides good traction on treated surfaces. But just how cheap it is?
The real cost is not just the cost of a bag of rock salt. The real cost must include the hidden costs. Excess road salt kills trees and plants. It damages the environment and contaminates waterways. Salt corrodes metal (eg, cars, trucks, bridges, etc.) and causes concrete, asphalt, and wood to deteriorate over time.
Rock Salt – A “Forever Contaminant”
Rock salt (sodium+chloride) doesn’t go away. Harmful effects linger in the environment and are compounded year after year. After a storm, excess road salt seeps into the soil, below the ground, and into our waterways. Road salt applied to roads, sidewalks, and parking lots is pushed onto lawns, shrubberies, and other surfaces when these areas are cleared.
Too much rock salt means that:
• Trees and plants lose water when salt is in the soil, causing nutrient loss.
• Soil becomes more compacted and degraded.
• Tree roots are suffocated.
• Trees and plants become more vulnerable to insects and disease.
• Salt can be toxic to wildlife, freshwater fish, and aquatic organisms, and harmful to pets.
• The health of our waterways is compromised, including drinking water: In 2021, the US Geological Survey (USGS) found increasing chloride concentrations in the Cambridge Reservoir and other MA waterways, in part due to rock salt.
How Much Road Salt is Enough?
Less is better. One 12-oz mug of rock salt is enough to treat a 20-foot driveway or 10 squares of sidewalk. Applying more rock salt on sidewalks and driveways does not achieve faster melting or more melting. The melting power of rock salt works when there is a space between granules. When rock salt is applied too thickly and in clumps, it melts only the contact layer of snow or ice. It does nothing to melt the rest.
Tip: If rock salt is crunching underfoot, it’s too much and it’s not working.
How can We Minimize the Harmful Effects of Rock Salt?
Follow “Smart Salting” practices.
- Apply less rock salt, with spacing between granules.
- Remove excess salt from treated surfaces after storms and save for the next storm.
- Choose footwear with good traction or buy an over-shoe wearable (eg, cleats).
- Protect pets by wiping off salt from dog paws after walks or put on dog booties.
- Hire contractors who minimize the excess use of road salt, who shovel and plow before deicing, and who keep piled snowbanks away from trees and plants as much as possible.
- When winter is over, test the soil. The UMass Soil & Plant Nutrient Testing Laboratory can perform a routine soil test and make fertility recommendations. Cost: $20.
- Hire a landscape contractor who specializes in lawn and tree repair due to excess salt.
- Plant salt-tolerant trees such as white and red oaks, paper birches, grey birches, honey locusts, horse chestnuts, and Japanese lilacs.
Over salting winter roads, sidewalks, and other surfaces is unnecessary and harmful. Using a Smart Salt approach is beneficial, protects the environment and our drinking water, and saves money.
Anne K Harrington is a Watertown writer and artist. Trees for Watertown is a 501(c)3 all- volunteer citizens organization dedicated to the greening of Watertown by planting, promoting and protecting Watertown’s urban forest. Learn more at TFW’s Facebook and Instagram pages (search “trees for watertown”) or visit TFW’s webpage (treesforwatertown.org)
Terrific article. Thank you.