Plants and Deicers
When deicers are used plants are at risk. The fate of your landscaping should be considered when making a choice of which deicer to use.
Salt is the least expensive material available. It is effective to approximately twenty degrees but can damage soil, plants and metals. Potassium chloride can also cause serious injury when washed or splashed on foliage. Both calcium chloride and potassium chloride can damage the roots of plants.
Plants that are especially susceptible to slat damage are: deciduous trees such as Green Ash, Hickory, Sugar Maple, Red Maple and Tulip Polar; conifers such as Norway Spruce, Balsam Fir, Hemlock and White Pine; shrubs including Dogwood, Hawthorn, Rose, Spirea and Redbud; and grasses including Kentucky Bluegrass and Fescue. While magnesium chloride is widely used, most people complain that it can transform ice into a slippery, slimy surface and the granules can act like ball bearings reducing traction.
Urea is a fertilizer that is sometimes used to melt ice. It is much less corrosive than salt but it can still contaminate ground and surface water with nitrates. Urea can damage plants if overused. And it is only effective when the temperature is above twenty degrees.
Some recommend the use of urea as a safer alternative to deicing products, arguing that it does not contain chlorides and the nitrogen, will help fertilize your yard when it washes off. Actually urea-based deicing products maybe a poor choice. Urea is fairly expensive and performs poorly when temperatures drop below 15°F. More importantly, the application rate for urea during a single deicing is ten times greater than that needed to fertilize the same area of your yard. Very little of the urea will actually get to your lawn- most of it will end up in the storm drain. Given that nitrogen is a major problem in water shed pollution, it may not make sense to nitrogen-based products like urea for deicing.
Calcium magnesium acetate or CMA is a newer product that is made from dolomitic limestone and acetic acid which is the main compound found in vinegar. CMA works differently than other materials in that it does not form a brine like salts but rather helps prevent snow particles from sticking to each other. While CMA has little effect on plant growth or concrete, the product works best when temperatures remain about twenty degrees.
All of these products are acceptable for use. Limited use of any of these products should cause little damage to plants. Problems accumulate when they are used excessively and there is not adequate rainfall to wash or leach the material from the area. It is still best to remove the snow and ice by hand when possible and spot treat with the ice melts reducing use.
If damage from deicers is going to occur it will not be noticeable right away. Problems will not appear until spring when the plants and grass along the walks may be dead. All products will have some effect on the environment.
Ice melting products work by first attracting moisture and forming a liquid, then as the liquid flows over and under the ice it causes it to melt. The rate of melting depends on how fast the chemical reacts to the existing moisture. When temperatures drop there is less water available and melting is slowed or inhibited.
Both sodium chloride (salt) and calcium chloride are very corrosive and can damage lawns, trees and shrubs. Ice melting materials that are less corrosive are: urea (fertilizer), potassium chloride (KCL), and calcium magnesium acetate (CMA). However, these materials are only effective down to approximately 20F and they are more expensive to use. The least effective of the three is the urea. Urea is a fertilizer and is required in large amounts to melt ice, giving rise to the potential that surface and ground water may be polluted.
Damage to plants can occur from runoff when using these products. In the spring, look for a browning of foliage, stunted growth and sections that die back. You may find these especially along walks, driveways, and roads. If you suspect deicer damage you may be able to confirm it with a soil test. Flush the affected area with plenty of water.
A study at the University of Wisconsin-Madison looked at the effects of several deicing products on Kentucky Bluegrass. The study showed that extensive use of potassium chloride (KCl) has the potential of inducing plant damage through nutrient imbalances and/or excessive amounts of soluble salts.
These results suggest that potassium chloride (KCl) is not preferable to sodium chloride (NaCl), calcium chloride (CaCl), and magnesium chloride (MgCl) as a deicer since potassium (K) is an essential plant nutrient. The least impact on turf grass was found when magnesium chloride (MgCl) was applied.
A similar study was performed at Iowa State University that also included Urea. Urea is 46% soluble nitrogen. Plants and turf grass are sensitive to sudden surges of undiluted urea that can occur after a winter build-up followed by spring thaws. In the Iowa State University study, urea at the lowest recommended deicer rate caused the slowest response of color development. The ISU study also showed some delay in turf grass color development when the other deicers were used at their recommended rates. Color development rates were delayed even more when the deicers were used at double their recommended rates.
Potassium chloride (KCl) and urea do not melt ice or snow at temperatures below 15ºF and are some of the least effective ingredients to be used in ice melters. In contrast, calcium chloride (CaCl) and magnesium chloride (MgCl) continue to melt ice and snow well below -10ºF.
Potassium Chloride and Urea are common ice melters that are often perceived as safe products to use around vegetation. Actually both would need to be used at a slightly higher rate of application, with Urea melting to 15o F and Potassium Chloride melting to 12o F. Urea is less corrosive and safer for use on concrete containing rebar and around steel structures.
Effective chloride blends can potentiate the positive effects of helpful compounds such as magnesium chloride while lessening any negative effects.