Navigating an icy walkway is one of the more treacherous winter activities so it makes sense that we reach for the cheapest and simplest solution—salt. However, sodium chloride is just as dangerous as ice, but for different reasons.
According to Environment Canada, Canadians use five million tonnes of salt per year. In 2001, the agency published a five-year study discussing how rock salt is damaging our ecosystems, soil, vegetation and wildlife—including your garden.
Salt damage often shows up in the spring when shrubs, trees and plants sprout leaves resembling drought stress with edges scorched brown or yellow. Other signs are stunted leaf or leaf curl as well as leaf drop. Salt-saturated soil will result in a gradual weakening of your garden, as the soil can't absorb enough water to allow for proper root development and becomes deficient in potassium and magnesium.
Don't assume that you can use salt in the winter and do a clean-up in the spring, either. "Desalinating soil can take a very long time," says Ron Berezan, an organic gardener for 20 years and operator of The Urban Farmer, Edmonton, Alberta. Treatment for too much salt usually involves repeatedly saturating the affected area with water to wash the salts further into the subsoils. Depending on the amount of salt that was used, this may just be relocating the problem. "Certainly avoiding using salt in the first place is the best solution," says Berezan.
Don't feel too smug if you have moved to using the more sophisticated de-icers. Many of the de-icers you'll find at the store aren't any better.
"Salt is salt," warns Joe Lamp'l, host of Garden Smart on PBS and author of The Green Gardener's Guide. "Too often we don't use de-icers properly. Their job is to loosen ice from below making it easier to shovel or plow, not remove ice completely."
Two of the most common "green" de-icers are made with chloride with the same results:
- Calcium Chloride (CaC12): Sold in flakes, pellets and liquid, CaC12 is less toxic to vegetation, but still toxic to pets, and corrodes metal. It also promotes growth of algae in waterways. It's three times more expensive than salt, but works up to -31° C/ -25° F.
- Magnesium Chloride: This de-icer is corrosive to metal, can burn plants, eats away concrete and is toxic to animals. You'll also need double the amount at double the price of rock salt. It works up to -25° C/-13° F.