By Joel M. Lerner
Saturday, February 13, 2010; E04
Local governments in the Washington area have been spreading massive amounts of de-icers for snow and ice removal. These materials can harm streams, rivers and the Chesapeake Bay as they wash from paving, and can harm pets, plants, wildlife and aquatic life.
Salts (chlorides), a common ice-melting agent, can be toxic to living things, especially when applied in excess, like this winter.
Rock salt (sodium chloride), a mined, native salt, is the best-known melting agent. It works fast and melts ice at temperatures as low as 20 degrees Fahrenheit. The coarse crystals can be broadcast onto pavements by hand or with a spreader. Of all de-icers, it most negatively affects plant growth -- but it is the most readily available and least expensive option. Apply two to four pounds per 100 square feet.
Another salt product is muriate of potash (potassium chloride), which is also used in fertilizer. Applied as recommended, it melts ice and won't hurt plants. It melts more slowly than rock salt but, with patience, provides superior results. Apply a maximum of three to five pounds per 100 square feet.
Calcium chloride, another salt, melts ice faster than the others and works at colder temperatures, down to 5 degrees Fahrenheit. It is one of the least harmful salts to concrete, but it damages plants. For plant safety, use it only when you can't find magnesium chloride, one of the newest materials to reach the homeowner market.
Magnesium chloride is your best bet if it's speed you want. Used as recommended, it won't harm paving or plants and is effective to minus-13 degrees Fahrenheit. You'll use less of this than other de-icers, applying it at a rate of one to two pounds per 100 square feet.
I like to use de-icers in conjunction with skid-proofing agents, which can keep a surface safe long after salt is dissolved. Some materials that offer traction on icy surfaces are sawdust, shredded corn cobs, peanut hulls, fine-ground bark, ashes, gravel, sand, cinders, perlite, vermiculite, kitty litter, straw and wood chips. All are environmentally friendly. These anti-skid agents do not dissolve in water and can be swept up for reuse. You can rake them into lawn or cultivate into planting beds without harming plants.
The most effective anti-skid products are cinders, coarse sand, tiny [one-eighth to one-quarter inch] crushed gravel and kitty litter. Among them, sand is the least obtrusive and easiest to clean up. These materials were used until the early 1960s, when the use of salt began.
Urea, synthesized from ammonia and carbon dioxide, is also a plant nutrient. It's effective to 25 degrees Fahrenheit. The drawbacks are that it promotes growth of algae when washed into rivers and streams and that it is slow-working. I consider urea to be more of a nitrogen source in fertilizer than a de-icer.
A product called Safe Paw is chemically similar to urea but contains nitrate inhibitors that reportedly bind its nitrates to soil and keep it out of water supplies. Safe Paw is advertised as pet-, child- and environmentally safe and does not contain chloride, so it doesn't damage concrete, lawn or plants.
Never use a fertilizer as a de-icer. Phosphorus and urea will run off into planting beds, and now is not the time to fertilize plants. It is also toxic to aquatic life.
If a little is good, more is not better. Do not over-apply salts. That's when they threaten plants and, used in extreme amounts, can damage concrete and mortar.
If you must use salt this winter, here are tips to help your plants survive:
-- Plant trees and shrubs 20 feet from roadways that are salted.
-- Don't shovel snow from salted walks onto plants.
-- Don't buy ice-melting products without knowing their ingredients.
-- Rely on rain and good soil aeration to help salt pass through soil with minimal damage.
-- Without rain, irrigate with about seven inches of water in spring (an inch a day for a week) if rainfall is inadequate.
-- Keep salt-sensitive plants like azaleas, crabapples, crapemyrtles, dogwoods, forsythias, American hollies, maples, rhododendrons, sweetgums and yews as clear of paving as possible.
Contact the University of Maryland Cooperative Extension Service for its free fact sheet "Melting Ice Safely." In Maryland, call 800-342-2507; from Virginia and Washington, 410-531-1757.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.