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The Science Of Salt

February 3, 2010
By Phil Cole

One of the biggest threats to our landscapes during the winter months is the use of de-icing salt on our roads and sidewalks. Not only can it wreak havoc on our automobiles, salt can eat away at certain pavements and a countless number of plants.

Salt damage to lawns and landscape plants are normally from two sources. It comes from salt used on city streets that may be splashed or spread on your yard, or from the use of an "ice melt" product that you may use to "de-ice" sidewalks or driveways.

The science behind de-icing or "rock" salt involves chloride and sodium, which when dissolved in water, become a toxic twosome to most plants. The sodium absorbs several minerals critical to plant life, while chloride interferes with photosynthesis, a plant's energy source.

But the damage from salt is not confined to our plants. In some cases, rock salt can crack concrete and even dislodge bricks from rigid bases. When concrete is improperly mixed and/or finished, melted snow and ice has the potential of being absorbed into the concrete. Salt naturally attracts more water and as soon as freezing conditions occur, the mix tends to expand more forcefully than water itself, causing separation in the concrete.

There are two defenses against this in concrete. One, assure an adequate compressive strength; and two, the mix must contain properly entrained air. Concrete that is ordered, mixed and installed properly can withstand several years of salt use.

The most efficient way to prevent damage caused by "de-icing" agents is to avoid salts altogether. The use of alternates such as coarse sand for traction or salt-free agents like calcium chloride or calcium magnesium will protect your landscape. Materials such as granular cat litter and sand don't melt ice and snow, but they can be used for traction. Mixing 50 pounds of sand and 1 pound of salt is effective and less damaging to plants and the surrounding soil. Choosing to use less salt materials on surfaces - especially in later winter when plants are coming out of dormancy and are more sensitive - is yet another way to protect your landscape.

If you must use salt, use it sensibly. Treat high traffic area only and create a temporary barrier like burlap around sensitive plants. In areas along major roads, sidewalks and institutions where salt is most commonly used, consider using higher salt-tolerant species of landscape plants.

In an article titled "Protecting Landscape Plants from Salt," Dr. Leonard Perry from the University of Vermont writes: "Salt-tolerant trees include larch, spruce, ashes, honey locust, oaks and poplar. Salt-tolerant shrubs include serviceberry, hydrangea, winterberry, shrub roses and arrow-wood viburnum."

Perry also states: "It is also important to note that dogwoods and hybrid roses are shrubs that are sensitive to salt."

Remember when determining landscape needs consider plants like honey locusts, ginkos, blue spruces, cotoneasters, junipers, Rosa Rugosas and several types of ornamental grasses around areas of your yard that may be susceptible to "de-icing" agents, namely rock salt.

This year we have already been stressed with the effects of snow and ice. As layers of salt go down on our streets and we work to remove ice from our sidewalks and driveways, protecting our lawn may be far from our minds. But with some planning and the use of less damaging products, we will save some back-breaking work this spring.

Phil Cole is a graduate landscape architect at the consulting firm of Hays Landscape Architecture Studio in St. Clairsville. For inquiries, call 740-695-6505 or visit www.hayslas.com.

 
 

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