Iowa State University Extension and Outreach 1/18/17
BALANCING LANDSCAPE PLANTS AND DEICING SALTS
Winter is here, and with it comes inclement, icy, snowy weather. Many Iowans use deicing salts to rid their properties of snow and ice, and deicing trucks and snowplows also spread chemicals on roads and streets. But these chemicals can have a negative effect on landscape plants. Are there precautions to take to avoid damage?
Deicing salts 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 also can create problems. Trees, shrubs, perennials and turfgrasses 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 amounts of 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. Soil structure is damaged by high levels of sodium. 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 die-back. Accumulation of salt in the soil over several years may result in the progressive decline and eventual death of plants.
Salt damage to evergreens results in yellowing or browning of needles and twig die-back. Evergreens near heavily salted roadways are often damaged by salt spray. Spray damage is most severe on the side of the plant nearest the street or highway.
The severity of plant damage depends upon the type of salt and other factors. Calcium chloride, potassium chloride and magnesium chloride are less harmful to plants than sodium chloride. The degree of salt damage also depends upon the amount of salt applied, soil type, amount of rainfall, direction of run-off and prevailing winds. The condition and type of plant material also is important. Healthy, vigorous plants are more tolerant of salt than poorly growing specimens.
Prudent use of deicing salts by homeowners can minimize damage to landscape plants. 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 abrasive materials, such as sand or kitty litter. 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 species.
Iowa State University Extension and Outreach horticulturists can help answer queries regarding landscape plants and deicing. To have additional questions answered, contact the Iowa State University Hortline at 515-294-3108 or hortline@iastate.edu.
