Rock Salt Damage to Evergreens

The Chemistry of Damage

• Most road salt is sodium chloride, the same compound as table salt. When dissolved in water, sodium and chloride ions separate. Chloride ions are drawn up by plant roots as soon as the ground thaws and winter dormancy ends, creating burn-like chemical damage to delicate feeder roots which can no longer play their part in the process of photosynthesis that feeds the plant. A high concentration of sodium ions keep soil from clumping, which creates heavy, compacted soil, making root uptake of water and air even more difficult, if not impossible. Ions further bond with soil ingredients like potassium and magnesium, preventing plants from absorbing these necessary nutrients.

Damage Symptoms

• Brown needle tips are usually the first sign of rock-salt poisoning. Browning appears in early spring on both existing foliage and new growth and extends to the full length of needles. Heavy watering can sometimes decrease or slow browning damage, but, even in wet soil, damaged roots cause plants to dry out and often die. The pace of damage is often determined by the manner in which it occurred.

Sources of Damage

• Diluted rock salt most frequently enters soil when it has been applied to nearby pavement. Because the salt-melted snow and ice runoff bonds so well to soil, damage may start in spring but persist throughout the growing season as plants continue to struggle in salt-tainted soil. Damage may first appear on the side of a plant closest to the runoff source, spreading as the season continues. Trees and shrubs planted close to road-salted streets may also manifest foliar burn on the side facing the salt source. Trucks and cars splash and spray salty runoff against nearby evergreens. Foliar spray damage is usually immediately evident in early spring and may not extend much beyond the directly damaged areas. Deciduous plants may display similar symptoms, producing bunches of leafless twigs commonly called "witches' brooms" along with burned foliage and reduced new growth.

Salt-Damage Reduction Strategies

• Using less salt is the most obvious way to reduce runoff damage, but the dangers of slippery walkways may outweigh possible plant damage. Calcium chloride- and nitrogen-based salts claim to be safer around plants. Adding sand to them lets you reduce the amount of salt while increasing traction and pedestrian safety. When planting new evergreens, locate them as far from runoff sources as possible; horticulturalists advise a separation of at least 50 feet between evergreen trees, shrubs and roadways. For new plantings, select evergreens known for salt tolerance. Depending on your location, you are likely to find members of the pine (Pinus spp.) and juniper (Juniperus spp.) families that tolerate some exposure to rock salt. Colorado spruce (Picea pungens, var. glauca) and other spruce varieties may be an option. Leach runoff from the soil around new and existing evergreens by watering them frequently and heavily in spring; this is an effective technique for well-drained soil. Shield existing plantings from traffic spray by building barriers of burlap, plastic, fencing or even window screen.