Salts in natural water systems vary from traces to toxic levels. While some 16 nutrients (salts) are found to be essential for plant growth, some soils have been found to contain salts in too high an abundance to support normal plant life. Salts containing sodium or chloride especially are injurious to landscape plants.

The double process of transpiration and evaporation (evapotranspiration) pulls the water through the soil along with some of the salts, but most salts are left behind in the soil.

“The combination of light, frequent watering and poor drainage results in salt accumulations that can cause what homeowners see as leaf burn and stunted growth,” says Ron Smith, North Dakota State University Extension Service horticulturist. “Other contributing factors to salt accumulation in the root zone come from applying too much fertilizer and a rise in the water table.”

As a sweeping generalization, states east of the Mississippi River, where rainfall is greater than 20 inches annually, seldom have salt problems in most landscape situations.

Going west of the Mississippi, higher soil and water salts are common. This creates problems to such an extent that special, expensive water treatments are needed to bring the salts down to a tolerable level for the economical growth of healthy plant material. If that is not feasible financially, then plants that have a high salt tolerance need to be selected for use in the landscape.

“In looking at what nature provides, we see that lilacs, ash, Russian olive, Juneberry, Black Hills spruce and several pine species, such as ponderosa, limber and mugo, are considered relatively salt tolerant,” Smith says. “What this means is that we can expect these plants to look halfway decent to the casual observer within a range of 6 to 12 deciSiemens per metre (dS/m), with the best looking ones being at the lower number.”

If the term deciSiemens per metre doesn’t translate, you’re not alone. One dS/m is equal to 1,000 electrical conductivity units, which equals 640 milligrams per litre or 640 parts per million (ppm). Envision the Fargodome as one brick equaling 1 ppm.

“Keep in mind that each ppm can be converted to pounds per acre in 6 inches of soil by multiplying by two,” Smith says. “When we say that a plant can look good at 6 dS/m, it is really in a pool of salt water with 3,840 ppm or about 1/2 ounce of salts per gallon.

“The salt situation in water and soil is not going to get better with time,” he says. “It is as good as it will ever be right now, so the answer is to try to select plants that are more tolerant of salty soils and water sources.”

NDSU Agriculture Communication