Which melting products are most effective, least harmful?
That's the word on snow and ice melt products from sand to rock salt to calcium chloride.
"Whatever you use, you need to use it wisely," said Mike Maddox, horticulture educator for Rotary Gardens and UW Extension. "You can't spray it haphazardly or it's going to cause problems."
Many people, from professional groundskeepers to average homeowners, use de-icing products incorrectly. They want to melt every last bit of snow and ice off the sidewalk, driveway or parking lot, but it's not practical, Maddox said.
It requires too much product, costs too much money, can harm vegetation and can damage concrete.
Dozens of snow and ice melt products are on the market.
Rock salt is the most commonly used product to melt snow and ice.
Calcium chloride is another popular choice.
Ammonium sulfate, potassium chloride and urea—chemicals found in fertilizers—also can be used.
So which one do you buy?
It depends on how much you're willing to spend, what you want it to do and what you don't want it to do, Maddox said.
People apply de-icing products for two main reasons: to melt snow and ice and to reduce the hazard of slipping, he said.
"If the latter is your main priority, sand really is best," he said. "But if you want to clear your sidewalk of snow and ice, use rock salt."
Among de-icers, rock salt is the least expensive and provides fair results. But it's effective to only about 15 degrees, Maddox said.
"There are other products you can buy," he said. "I don't buy them. I use rock salt."
While rock salt can damage to concrete and vegetation, it's the best option when used properly, Maddox said.
"I put down enough to break up the ice, and then I have to break it up manually," he said. "If your idea is to throw down a lot of salt and melt everything, you're going to have problems."
What do they use at Rotary Gardens?
"We use rock salt, and we use sand, and we shovel, shovel, shovel," Maddox said.
Rock salt can suck the life out of grass, plants and trees planted along sidewalks, driveways and roadways.
Because salt attracts water, it interferes with a plant's ability to draw water through its roots, Maddox said.
"If you put too much salt in the soil, it pulls water out of the plant tissue, causing it to burn," he said. "The plant just can't get enough water, and it dries out."
Salt also can deteriorate soil, breaking the bonds that hold soil together, reducing pore space and making it more easily compacted, he said.
"Without the pore space, roots can't grow," he said.
Trees planted along roads also are susceptible to damage from "salt spray" kicked up by vehicles passing on wet roads.
Salt spray dehydrates plant tissue, killing buds and twigs, browning leaves and needles and even causing dense clusters of shoots to grow from a single point, something more commonly known as witch's broom, Maddox said.
Maddox recommends homeowners rinse areas near plants and trees to flush away excess salt and reduce the potential for burning.
Rock salt also can damage concrete, subjecting it to pressure and causing it to crack.
Because it attracts water, salt can make concrete more saturated with water, spelling trouble when the water freezes, said Andrea Breen, a master gardener volunteer and engineer in the cement division at Lafarge North America.
"It draws more water into it, deeper into it," she said. "And then you have a harder freeze at a deeper level."
A good sealer can prevent water from penetrating concrete's surface, Breen said.
"Just by its nature, it wears out," she said. "But if concrete is properly placed and cured and sealed, we can minimize that."
While the majority of the most commonly used de-icers don't chemically "attack" concrete, magnesium-based de-icers do, Breen said. A chemical reaction causes the magnesium to replace the calcium in concrete, essentially breaking down the "glue" that binds the aggregate together.
Breen recommends homeowners sweep excess salt from their sidewalks and driveways or wait for a warm day to rinse them and dilute the salt.
Regardless of which de-icer people choose, it's important to read product labels and be judicious in applying the product, Maddox and Breen said. By using the minimum amount needed to break up snow and ice, people will cause the least damage to their plants and pavement, they said.
HOW IT WORKS
Salt lowers the freezing point of water, said UW-Madison chemistry professor Bob Hamers.
When you add rock salt—sodium chloride—to water, it dissolves and breaks into one sodium ion and one chloride ion, he said.
The ions disrupt the formation of ice crystals, Hamers said.
A compound that yields more ions would lower the freezing point of water further, he said. For example, calcium chloride (CaCl2) dissolves into three particles, one calcium ion and two chloride ions.
"The more ions, the better," Hamers said.