Salt damage on a Leyland cypress. Photo: Tom Ford
The winter of 2013-2014 may have been the worst in 30 years, and some property managers readily admit that they used two to three times more de-icing compound this winter than they had used in previous years. The accumulation of sodium chloride in the soil induces a chemical drought in plants resulting in the movement of water from plant tissues into the saline soil environment.
As a result of sodium chloride injury, property owners and landscape managers growing deciduous trees may see a reduction in green leaf coloration, smaller leaves with scorched and/or brown margins, thinning crowns with dying twigs and branches, and premature fall coloration. Growers of evergreen trees may notice the browning of needle tips, premature needle drop, and an overall weakening of the tree.
In order to mitigate the risk of salt injury in the landscape, grounds managers and property owners should first select salt tolerant species when planting in areas prone to road salt run-off and road salt deposition. Deciduous trees with good salt tolerance include: oaks, black locust, hickories, birch, Norway maple, buckeyes, ginkgo, honey locust, and elm.
If the selection of salt tolerant species is not possible, plan to irrigate the affected soils with clear water in an effort to leach the sodium chloride from the soil profile prior to spring growth. A generally accepted rule states that six inches of water directly applied to the soil will leach out 50% of the salt that has accumulated in the soil profile. On a per acre basis, this amounts to over 162,000 gallons of water per acre.
If leaching the soil at your site is impossible, consider making an application of gypsum (calcium sulfate) to the soil. The addition of calcium to the soil displaces the sodium and lessens the dispersion of soil particles and the loss of soil aggregates. Gypsum does not raise the pH of the soil and is usually applied at a rate of 40 pounds per 1000 square feet.