March 21, 2001
Stillwater Gazette
Betsy Halden

Salt injury to plants

Snow and more snow this winter. Each winter disturbance has left more snow and ice on our roads, walks, and lawns. City road trucks come by and plow and salt our roads to enable motorists to travel. But it is the road salt which can injure landscape plants. Salt causes plant injury if it accumulates in soil near the root system of plants. This can happen when salt-laden snow is plowed off streets, parking lots and sidewalks and onto adjacent landscapes.

For those of use who have tried to get the table salt out of a damp shaker we know that salt absorbs water. Rock salt, the most common deicing salt, exhibits the same property in the soil. It absorbs much of the water that would normally be available to roots. Thus, even when soil moisture is plentiful, high amounts of salt can cause a drought-like environment for plants.

Excess sodium in sod decreases plant health and vigor in several ways. High amounts of sodium causes soil to lose its capacity to aggregate into clumps. Then the soil easily becomes compacted. Access to water and oxygen are restricted and the roots cannot function to their full potential. Excess sodium also inhibits a plant from obtaining nutrients by tying up the plant’s nutrient transport system. The nutrient transport system provides magnesium and potassium, two elements that are essential for plants to make chlorophyll.

When salt is deposited on plants by spray from passing cars and trucks, salt may directly enter plant cells or the spaces between cell. One result is that buds and small twigs of some plant species lose cold hardiness and are more likely to be killed by freezing ;temperatures. In addition to the direct effects that slat has on plant growth, affected plants also suffer reduced vigor. They are susceptible to attack by insect pests and diseases and are more sensitive to adverse environmental factors such as drought and air pollution.

Symptoms: The common symptoms of salt injury resemble those caused by drought or root injury. Stunted, yellow foliage, premature autumn color, death of leaf margins and twig dieback are common. Conifers injured by salt spray have yellow or brown needles in early spring. If salt spray is the primary cause of needle damage, new growth will disguise the damage. If salt is also excessive in the soil, the new needles may also die after emerging. This can be lethal to the plant if it occurs several years in a row.

Strategies for prevention: The homeowner can use alternatives to salt. Sand or light gravel can be used on icy or snow-covered walks. Other alternatives that are not cost effective for road maintenance but could cut down on salt from driveways include mixing fertilizer with sand (2.5 – 3 lbs. Urea to 100 lbs. Of sand) or adding calcium chloride to sawdust or kitty litter in a 1:3 ratio.

Spring applications harshest: Salt applied to roads after the beginning of March is most detrimental to vegetation and should be kept to a minimum. Plants begin to break dormancy under the March sun and the roots are actively absorbing nutrients and water from the soil. These nutrients and the water will supply the imminent new spring growth. Of the plants. Toxic chloride ions are usually rapidly leached from the soil. But at this time they are most likely to be absorbed by the plant roots. Avoid piling salt and snow around plants or where the water from the melting snow will drain onto plants. If weather permits, or as soon as the snow does melt, use fresh water to flush the area around roots exposed to salt. Lastly, where salt exposure is likely, select plants that are tolerant of salt. For suggestion of salt-tolerant plants, call INFO-U at 612.624.2200.

Other timely information for gardeners in March is available in INFO-U. Dial 612.624.2200 and then select one of the following topic numbers: 507 – Pruning trees; 548 – Hiring tree services 560 – Oak wilt prevention; 563 – Pruning shrubs; 570 – black knot prevention.

Betsy Halden is a Master Gardener with the University of Minnesota Extension Service. University of Minnesota Extension Service materials were consulted in the preparation of this column. You can reach Betsy Halden at eahalden@comcast.net