Ice Melters and Their Effects on Plants
Ice Melters and Their Effects on Plants
We are approaching the time when icy streets and sidewalks may again make walking and driving hazardous. Ice melting products can help keep us safe. However, these products vary in their ice melting abilities and in their safety to nearby plants. There are 5 main materials that are used as chemical de-icers: calcium chloride, sodium chloride (salt), potassium chloride, urea, and calcium magnesium acetate.
Calcium chloride is the traditional ice-melting product. Though it will melt ice to minus 25 degrees F, it will form slippery, slimy surfaces on concrete and other hard surfaces. Plants are not likely to be harmed unless excessive amounts are used. It is fast acting, and more effective than rock salt. Can damage grass and plants if overapplied.
Rock salt is sodium chloride and is the least expensive material available. It is effective to approximately 20 degrees F but can damage soils, plants and metals, and paving surfaces.
Magnesium chloride is effective down to minus 13 degrees F. and is more effective than sodium chloride. Can damage plants if overapplied.
Potassium chloride is effective down to 25 degrees F. and can also cause serious plant injury if overapplied.
Urea is a fertilizer that is sometimes used to melt ice. Though it is only about 10% as corrosive as sodium chloride, it can contaminate ground and surface water with nitrates. Urea is effective down to 10 degrees F., but works better between 25-30 degrees F. It can damage plants if overapplied.
Calcium magnesium acetate (CMA), a newer product, is made from dolomitic limestone and acetic acid (the principal compound of vinegar). CMA works differently than the other materials in that it does not form brine like salt but rather helps prevent snow particles from sticking to each other or the road surface. It has little effect on plant growth but can damage concrete surfaces. It is less corrosive than chloride products. Performance decreases below 20 degrees F.
Limited use of any of these products should cause little injury. Problems accumulate when they are used excessively and there is not adequate rainfall to wash or leach the material from the area. Since limited use is recommended, it is best to remove the ice and snow by hand when possible. When they are applied, practice moderation. We are often prone to over applying just to make sure the ice and snow melts. Keep in mind this can damage concrete surfaces as well as the plants and grass growing along the walks and driveways. These problems are normally latent and do not show up until spring or summer.
Salts can injure plants in several ways. The chloride ion is considered the most toxic element of deicing salts, causing much of the direct plant tissue damage. When salt sprays from puddles onto plants as cars drive by, it may scorch leaves or kill buds and twig tips on deciduous plants, especially during spring. Pines in general are especially noted for their sensitivity to roadside deicing salts. When affected, pine needles may become pale green, yellow, or brown in late winter. If dying vegetation is on the side of the plants facing the road or driveway, the damage has likely been caused by salt spray.
Accumulation of salt in the soil also makes it difficult for plant roots to absorb water. Excess sodium affects soil structure, and may result in poor infiltration and increased erosion. The sodium ions can displace essential plant nutrients, decreasing soil fertility. Salt accumulation in soil will also inhibit seed germination of grasses and wildflowers.
The level of damage varies, depending on the concentration of salts in the water running onto your plants, the amount of snowfall, the timing of rains that may help wash off the foliage, the type of soil, and the condition of the plants. Healthy, mature plants that are not drought-stressed will withstand salts better than newly established, young plants.