The Assault of Salt
Most of the de-icers we use on roads and sidewalks are simply salt—common, everyday table salt. Sounds innocent enough, right? But when salt mixes with snow and melts into the soil, the salt begins its dirty work underground, preventing water and nutrient absorption by garden plants.
Above ground, the results are brown lawns with bare spots, spring bulbs that are undernourished and may not flower, crabgrass, tired-looking rose bushes, scorched maple leaves, and pine trees with brown needle tips. Salt products also damage waterways when they wash away in the spring.
The dirt on salt? It’s out of sight, but not out of our soil—and it can damage the plants which grow in that soil!
Salting the Soil in Winter
Here’s the big picture: In just 50 years, our country has gone from using sand and cinders (think traction) to spreading a mind-boggling 10+ million tons of salt onto roadways annually, which is enough salt to fill Soldier Field’s playing area to a depth of 10 feet deep over 500 times!
All that salt is on the move: sprayed into the air by high-speed traffic when wet, kicked up as dust when dry, splashed out of puddles, plowed into snow banks, and melting into streams and rivers, city sewers…and our yards.
Homeowners add to salt’s assault on soil by de-icing steps, sidewalks, and driveways, then shoveling or snowblowing salt-filled snow directly onto plants and trees.
Plants are 90 percent water, and they depend on water moving from the soil up to their roots and leaves. Excess salt stalls and prevents this movement, literally dehydrating the plants growing in that soil.
Some common landscape plants are particularly susceptible to salt damage:
- Sugar maples and red maples, both beloved in residential areas, may show leaf scald.
- Pine trees, especially white pines, are highly salt-sensitive and are attacked externally by airborne salt all winter. Watch for needles’ telltale brown tips in spring.
- Rose bushes, Japanese maples, and spirea—prized by gardeners—don’t grow well as salt levels rise.
- Lawn: Salt and other de-icers can burn or kill lawns, often leaving bare soil (but happy crabgrass).
NIMBY (Not In My Beautiful Yard)
What are your de-icing alternatives? The search is on for scientists to find a de-icer that has no environmental consequences. In the meantime, use products sparingly. Spreading sand is the safest alternative for your soil and plants.
But if you do require a de-icer, the least harmful salt product is potassium chloride (KCI). Read manufacturer’s directions and consider the potential risks to your soil and plants when choosing which one to purchase. Here are some of your salt de-icing choices:
- Everyday table salt: Sodium chloride (NaCl), sold as “rock salt”, is the cheapest and most popular de-icer. However, NaCl stops working around 20º F, and it damages plants by releasing high amounts of chloride.
- Potassium chloride (Kcl): the best choice for northeastern Illinois if you must use a de-icer, because it causes the least amount of damage to soils and plants. But it only melts ice and snow at temperatures above 15° F. Potassium chloride ice-melter is available at most gardening and discount retail stores.
- Calcium chloride (CaCl2): your second best salt choice based the impact on soil and plants, and works below 15° F. However, CaCl2 can irritate skin, damage concrete, and corrode metal.
- Calcium magnesium acetate: known as CMA, may cost four to five times as much as NaCl. Try to avoid this product. Made from the reaction between acetic acid (the acid in vinegar) and lime, it appears to pose fewer impacts to plants, but if washed into waterways it may cause fish toxicity problems.
The best option of all for plant and soil health is to use sand to provide traction. Sand does not damage soil or plants. However use sand sparingly, because excessive sand can accumulate in your soil, raising the level of your lawn or flower bed; and sand-laden runoff can clog up storm sewers and choke creeks and streams.
What’s a Gardener to Do?
- If you can, halt the salt! Limiting chemical de-icers to reduce icy patches that resist shoveling.
- Sand is a good substitute for salt, used sparingly.
- Shovel or snow-blow soon after it stops snowing and before the snowy slush freezes, so that little or no de-icer is needed.
- Check the current and predicted outdoor temperatures before you use de-icers, in case it’s too cold and they prove ineffective.
- Shovel snow thoughtfully. Avoid piling salt-laden snow in garden areas or beneath your prized trees and shrubs.
- Even if you take action to reduce de-icer applications, there still may be areas in your landscape where impacts are simply going to be unavoidable. Luckily, some plants are relatively tolerant of salty soils, including Little Bluestem, Sweet Gum, and Bald Cypress (more salt-tolerant plants can be found via The Morton Arboretum and this list from the Virginia Cooperative Extension).
- Consider moving your favorite salt-sensitive landscape plants away from salt-prone areas in your yard.
- Share what you know. Your neighbors may be over-salting, too!
Special thanks to Patrick Kelsey for his scientific contributions.