According to Cornell University Cooperative Extension, salts used for deicing can cause problems for trees and shrubs, and some salts can even cause corrosion of sidewalks and driveway paving, as well as irritation to pets and moist human skin. Here's a guide to the different types of deicing salts available in our area, and the best uses for each.
Sodium Chloride: This is similar to common table salt. It is also known as rock salt. It is the most commonly available type of deicing salt, and is the least costly. Sodium chloride does not damage concrete. It is easy to apply. There are downsides, however. It can damage trees and shrubs, and it does not melt ice at temperatures below 15*F. In fact, it is most effective at temperatures in the mid-20s. Sodium chloride also causes pollution problems in lakes, streams and rivers, as it dissolves and releases chloride ions. If you deice with sodium chloride, apply sparingly and make sure the snow and ice melt does not run off into storm drains or streams.
Potassium Chloride: This is used in the production of fertilizer, and it can be used as a deicing salt. Because of rapidly rising world fertilizer prices, potassium chloride is currently the most expensive of the four common deicing salts, and declining in both availability and popularity as a deicing agent. It does not irritate moist skin as some other salts can. If used in moderation, it is relatively safe for trees and shrubs. Like sodium chloride, potassium chloride is only effective at temperatures above 15*F. It is sometimes mixed with other salts to make it more effective as a deicer at lower temperatures. It can also pollute groundwater, lakes, rivers and streams with the chloride ions it releases when dissolved in water, so protect against runoff into storm drains, streams, and open bodies of water.
Calcium Chloride: This deicing salt is popular in extremely cold areas. It can melt ice at temperatures down to -25*F, due to its exothermic reaction that produces heat. It is relatively safe to use around trees and shrubs, but it can irritate the skin, and the unprotected pads of dogs', cats' and other animals' feet. The cost is approximately three to four times the cost of sodium chloride, though it is often a more efficient melting agent and may need to be applied less often. Calcium chloride can damage concrete, if used repeatedly and in heavy applications. It can cause environmental pollution similar to the other salts, if allowed to run off into lakes, rivers and streams.
Magnesium Chloride: This salt acts in a manner similar to calcium chloride. In colder climates, it is often applied to roads as a brine solution prior to precipitation, as it lowers the freezing point of new moisture. It helps prevent new snow and ice from sticking to the surface of the road, making it easier for snowplows to do their job. It can melt snow and ice down to -15*F. It is relatively safe for vegetation and pets, if used in moderation. Magnesium chloride is less corrosive to concrete than calcium chloride. It is the least polluting of these four types of salts. Magnesium chloride is increasingly available, and the cost ranges in the middle of the pack of these four deicing salts.
Cornell University Cooperative Extension master gardeners in Allegany and Cattaraugus counties have more information on deicing salts and other garden and home grounds information. To contact a master gardener in Cattaraugus County call 699-2377 extension 127 or email firstname.lastname@example.org, for Allegany County call (585) 268-7644 extension 23.