For this week's column, I'll paraphrase an article from one of our Kansas State University Extension horticulture specialists, Ward Upham. He directs the Rapid-Response Center, which assists Extension agents across the state on horticulture questions and inquiries when we occasionally need supportive assistance. In light of the winter conditions across the area, his comments are timely and noteworthy.
Carefully limited use of de-icers can boost sidewalk and driveway safety, yet cause little to no injury to concrete surfaces or nearby plants. Unfortunately, though, de-icers seem to be the kind of product that makes people think, "If a little is good, a lot should be even better." That can lead to problems — which typically won't show up until spring or summer.
Often, the worst cases result when buyer-appliers don't understand the products' intended use. De-icers are not a snow shovel substitute! When possible, the best way to promote safe outdoor conditions is to shovel as soon as a storm stops. That way, you won't have the compacted ice that results so quickly when someone walks or drives on new-fallen snow. You won't get ice from later melt-freeze cycles, either.
Once ice enters the picture, however, applying a de-icer can help loosen snow and ice from pavement surfaces. That, in turn, can make shoveling easier. In general, the thinner and newer the ice buildup, the more effective the de-icing is likely to be.
Breaking the bond between ice and pavement also helps you do a complete enough job that you don't leave slick spots or chemical-laden slush behind. Those things can become hazards for future pedestrian safety. In many cases, they also can lead to pitted paving and burned plants.
Another factor that leads to overuse is that no de-icer is perfect on all counts. Plus, the five main ingredients most often used as chemical de-icers have differing abilities. People who don't know what they're buying can expect too much from a particular product. So, when they don't achieve the results they want, they often try applying "just a little more."
Upham outlined the abilities of the major de-icer ingredients as follows:
Calcium chloride — the traditional ice-melting product. It will continue to melt ice down to temperatures of 25 degrees below zero. It gets to work fairly quickly, too, because it attracts its own solvent and then gives off heat when it reacts to the water. But, it forms slippery, slimy surfaces on concrete and other hard surfaces. And, excessive use can harm plant roots.
Sodium chloride (rock salt) — the cheapest option. It remains effective down to about 12 degrees. However, it can damage not only plants but also metals and soils.
Potassium chloride — a naturally occurring material also used as a fertilizer and a food-salt substitute. It can melt ice when temperatures are in the teens. It's not as widely available as the other active ingredients, however, because the compound's high salt index can lead to serious plant injury, above and below ground.
Urea (carbonyl diamide) — a fertilizer sometimes used to melt ice in temperatures as low as 21 degrees. Urea is only about 10 percent as corrosive as sodium chloride, and it's less likely than potassium chloride to burn plants. Nonetheless, it brings its own risks. Excessive urea can contaminate both ground and surface water supplies with nitrates.
Calcium magnesium acetate (CMA) — a newer and typically more costly product made from dolomitic limestone and acetic acid (the principal compound of vinegar). Its performance decreases below 20 degrees. But, CMA has little effect on plant growth or concrete surfaces. CMA also does not form a brine, as the chlorides do. Instead, it helps prevent snow particles from sticking to each other or to paved surfaces.
"A final problem is that after people shovel, they sometimes distribute more de-icer, as if it were designed to provide traction for walking. Big mistake," Upham said. A scattering of sand is the traditional way to create traction. But, a sprinkling of natural clay kitty litter has fans now, too. Cracked corn and bird seed are gaining notice as "green" possibilities that both provide traction and serve as winter bird food.
One problem with bird seed, of course, is that anything the birds miss now could sprout and grow into a weed — a plant out of place — next spring. Kitty litter, on the other hand, can turn into a slippery mess as it absorbs de-iced moisture and quickly refreezes, but then melts later in rising temperatures. Any traction-adding material is also likely to end up stuck in shoe treads and tracked into your house and will act as a floor-damaging abrasive. Traction adders can seem necessary to avoid being liable for accidents.