Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

12/22/03

Contacts:
Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning Dec. 26, 2003

Deicing Compounds and the Home Landscape

By Richard Jauron
Extension Horticulture Specialist
Iowa State University

Snow and ice are headaches for motorists and pedestrians. To prevent accidents on slippery surfaces, highway departments, businesses and homeowners use deicing compounds to melt ice and snow on roadways, parking lots, sidewalks and driveways. While deicing materials improve travel conditions, they can damage automobiles, concrete surfaces and landscape plants.

Deicing Compounds
Most deicing materials are salts that melt ice and snow by lowering the freezing point of water below 32 degrees F. However, a few other materials can also be used on icy and snowy surfaces. Advantages and disadvantages of several commonly used deicing agents are discussed below.

Sodium chloride (NaCl) is commonly known as table salt or rock salt. It's the least expensive and most widely used deicing compound. Sodium chloride is most effective when temperatures are above 15 degrees. Unfortunately, NaCl is highly corrosive and can damage plants. High levels of sodium are also detrimental to soil structure.

Calcium chloride (CaCl2) dissolves and works quickly. It also is effective in extremely cold weather. Calcium chloride melts ice and snow down to 20 degrees below zero. It doesn't leave a white, powdery residue on carpets and floors. CaCl2 is highly corrosive to concrete and metals. It is slightly less damaging to plants than sodium chloride.
Potassium chloride (KCl) is a naturally occurring material used as a fertilizer (0-0-60) and deicing compound. Potassium chloride is effective to 20 degrees. It's highly corrosive, but less damaging to plants that sodium chloride.

Magnesium chloride (MgCl2) effectively melts ice and snow down to 5 degrees. MgCl2 works quickly and doesn't leave a powdery residue.

Calcium magnesium acetate (CMA) is a salt-free deicing compound made from dolomitic limestone and acetic acid. CMA is effective to 20 degrees. It causes little or no damage to landscape plants and is less corrosive than deicing salts. Unfortunately, CMA is quite expensive (approximately 20 times more expensive than sodium chloride) and is not widely available.

Abrasive materials, such as sand and cinders, don't melt ice and snow, but improve traction on slippery surfaces. While these materials are inexpensive and cause little harm to plants, they are often tracked indoors and may damage floor surfaces.

Effects of Deicing Salts
Deicing salts (NaCl, CaCl2, KCl, and MgCl2) can damage landscape plants when excessive amounts accumulate in the soil. The most serious damage typically occurs near major streets and highways where salt from run-off accumulates in the nearby soil. Excessive use of salt by homeowners can also create problems. Trees, shrubs, perennials and turf grasses are susceptible to salt damage. Additionally, spray from passing vehicles can damage roadside plants, particularly evergreens.
Salts affect plant growth in several ways. When high levels of salt are present in the soil, plants are unable to absorb sufficient water even though soil moisture is plentiful. Plants suffer a salt-induced water shortage termed "physiological drought." High levels of salt restrict the uptake of essential nutrients by plant roots. Excessive amounts of sodium and chloride ions in plant tissue are toxic to many plants. High sodium levels damage soil structure. Salt deposited directly on plant foliage can cause dehydration of plant tissue.

The symptoms of salt injury to deciduous trees and shrubs include stunted growth, marginal leaf scorch, early fall coloration and twig dieback. Accumulation of salt in the soil over several years may result in progressive decline and eventual death.

Salt damage to evergreens results in yellowing or browning of the needles and twig dieback. Evergreens near heavily salted roadways are often damaged by salt spray. Spray damage is most severe on the side of the plant nearest the highway.

The severity of damage depends on many factors. The more salt that is applied to icy and snowy surfaces, the greater the runoff into nearby soils. The degree of salt damage also depends on soil type, amount of rainfall, direction of run-off, and prevailing winds. The condition and type of plant material is also important. Healthy, vigorous plants are much more tolerant of salt than poorly growing specimens. White ash, honeylocust and Norway maple are salt tolerant, while sugar maple, hackberry, littleleaf linden and white pine are highly sensitive.

Salt Injury Prevention
Homeowners can minimize salt damage by using deicing salts prudently. Before applying salt, wait until the precipitation has ended and remove as much of the ice and snow as possible. Use deicing salts at rates sufficient to loosen ice and snow from driveways and sidewalks, then remove the loosened ice and snow with a shovel. (Deicing salts need to be applied at much higher rates to completely melt ice and snow.) Mix salt with an abrasive material. Fifty pounds of sand mixed with one pound of salt works effectively. Avoid piling salt-laden snow and ice around trees and shrubs. While the amount of salt applied to major roadways cannot be controlled, steps can be taken to minimize damage. As soon as the ground thaws in early spring, heavily water areas where salt accumulates over winter. A thorough soaking should help flush the salt from the root zones of plants. If possible, alter the drainage pattern so winter run-off drains away from ornamental plants. When planting trees near major streets or highways, select salt tolerant tree species.

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Editors: There is no photo available for this week's column.

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