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Chemical de-icing materials can damage plants

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By Dennis Morgeson

We haven’t had to worry about this yet, but I thought it would be a good time to discuss it before it is needed. If you like to put salt and de-icer on your sidewalks, drives and steps, you must take care not to damage valuable landscape plants. Generally, physical removal of ice and snow is better for the landscape as long as you don’t pile it on your plants. However, many people aren’t physically able to shovel snow and ice. In this case chemicals are needed to keep walkways safe.

The most common chemical used for de-icing roads and sidewalks is rock salt or sodium chloride. This material is relatively inexpensive and can be purchased at most department and hardware stores.

Calcium chloride is the second most commonly used de-icing material.  Calcium chloride produces heat as it dissolves, so it is often added to rock salt to increase the effectiveness of the salt down to the low 20s.  Calcium chloride by itself can melt ice and snow down to -20 degrees.

Calcium magnesium acetate is the third most commonly chemical de-icer and is made by mixing dolomitic limestone and acetic acid (the principle component of vinegar). This mixture is about as effective as rock salt in regards to ice melting but isn’t as harmful to plants, soil, concrete and metal surfaces. Two other chemicals are also used to melt ice, potassium chloride and urea. Although these both are used as fertilizers, it doesn’t mean they won’t damage your landscape.

The build up of these chemicals on plant surfaces and in the soil can greatly affect landscape plants. The damage on evergreens is the most noticeable because their leaves are still present when salt spray and salt laden snow are thrown on and around the plant. The leaves of evergreens turn brown generally slowly over several days after contact. This isn’t the only effect however, buds and twigs can be damaged on both evergreens and deciduous plants. In this case re-growth in the spring may originate from a single point forming clusters of shoots or “witch’s broom”.Buildup of de-icing materials in the soil causes the most serious problems. These materials can buildup over one season or over several seasons. High salt and chemical levels in the soil make roots unavailable to take up water and nutrients. The symptoms will include wilting, even when the soil is moist, leaf burn or needle tip burn, stunting or lack of vigor, and/or deficiency symptoms for one or more plant nutrients. The structure of clay soils can be altered so much that it may not be able to support any plant life.

To help keep your landscape looking nice and safe there are a few simple things you can do. Obviously limiting your plant’s exposure to these harmful chemicals is going to go a long way to keeping them healthy. Flushing the soil with a large amount of water will help leach the chemicals out of the soil. This should be done after it warms up and the ground has thawed. If we have a snowy winter you may have to do this several times in a season. If you have a choice of which de-icer you are going to use, calcium magnesium acetate or calcium chloride are generally the safest. Avoid rock salt. As with any chemical, read and follow all label directions.

The use of abrasive materials such as kitty litter, sand and sawdust can help give you traction on icy surfaces if you aren’t willing to use chemical de-icers. The darker colors of these materials will absorb solar radiation and increase the melting speed of ice. You can also mix these materials with chemical de-icers to increase their effectiveness.

Fertilizers will effectively melt snow; however they can and will damage concrete and metal surfaces. Overuse can also damage landscape plants severely. They can cause extremely rapid growth in the spring which can jeopardize overall plant health throughout the year.

For people living close to roadways it can be unavoidable that their plants come into contact with de-icing materials. There are several plants that are relatively tolerant to high levels of these chemicals and plants that are very sensitive to these chemicals. The following trees and shrubs are relatively resistant: white ash, honey locust, black locust, eastern red cedar, Colorado spruce, Austrian pine, winged or burning bush euonymus, pfitzer juniper, mock orange, sumac and rugosa rose. The following species are very sensitive to salt and should not be planted near roadways: arborvitae, beech, holly, dogwood, hemlock, scotch and white pine.
Year round plant care such as pruning, watering, fertilizing and weed control will promote plant health which will make your plant more tolerant to salt levels. However, for the overall health of the landscape, the goal should be to eliminate chemical de-icers from home use.
The next time it snows, burn some calories and shovel that snow from you sidewalks and drives. It will make you and your landscape healthier.  Happy gardening!