~by Richard Jauron and Greg Wallace, ISU Extension & Outreach
AMES — Winter has officially begun in Iowa, and with it come snow and ice. Life keeps rolling in winter, which means the application of deicing salt and other measures to keep roads open and prevent slickness and falls on hard outdoor surfaces. Unfortunately, these measures can have negative effects on the landscape.
Here are some tips from Iowa State University Extension and Outreach horticulturists on how to handle winter deicing chemicals. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.
What effects do deicing compounds have on landscape plants?
Deicing salts, such as NaCl, CaCl2, KCl and MgCl2, can damage landscape plants when excessive amounts accumulate in the soil. 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. Soil structure is damaged by high levels of sodium. Salt deposited directly on plant foliage can cause dehydration of plant tissue.
What are the symptoms of deicing salt injury to trees and shrubs?
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 often are damaged by salt spray. Spray damage is most severe on the side of the plant nearest the highway.
How can I prevent damage to trees and shrubs from deicing salts?
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 abrasive materials, such as sand or kitty litter.
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 zone 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. Bur oak, northern red oak, honeylocust, northern catalpa, Kentucky coffeetree, horse chestnut and eastern red-cedar are salt tolerant tree species.
