Over 500,000 tons of deicing salt are applied to our state and municipal roads each year. Safe winter travel is important; however using salt on roads, driveways and walks has consequences. While most people are only too aware of the corrosive effects of salt on automobiles and road surfaces, the negative (and sometimes irreparable) impact it can also have on our landscapes is often overlooked.
As dissolved road salt washes into nearby soils, its two components – chloride and sodium – separate and act individually to injure plants. Chloride enters the sap stream through the roots and makes its way to actively growing portions of the plant, such as shoot tips, and stunts growth. Meanwhile, sodium depletes the soil of nutrients and beneficial microorganisms essential to plant health. Above ground, dormant buds are killed as salt spray from passing vehicles penetrates the foliage. With this overall reduction in vigor, plants are more susceptible to pest and disease infestations and more likely to be damaged by other stresses throughout the year, such as summer droughts and storms.
To make matters worse, salt doesn’t stay where you put it. Wind can carry salt from the roads to bordering shrubs, lawns and trees. It is not uncommon to see trees or shrubs with brown needles or leaves just on the side facing the road. Strong winds have been known to carry salt hundreds of feet away from its source. As salt dissolves, it enters the soil; any lawns or plantings near salted pavement are likely to receive a heavy dose.
Although abandoning the use of deicing salts after snow storms is obviously unreasonable, there are steps you can take to minimize potential damage to your landscape this season. For walkways and driveways, combining your deicing salt with sand, light gravel or cinders will provide adequate traction for travelers while decreasing the overall use of salt. There are also deicing agents, including potassium acetate and calcium magnesium acetate, that don’t have the detrimental effects on plants that traditional products do. An interesting development in sustainability, white beet extract leftover from sugar production is being used as an additive to road salts. The extract significantly reduces runoff due to its tacky composition and also keeps salts effective in much lower temperatures.
When you cannot control what’s being applied, flushing exposed soils with tap water as soon as the snow melts will greatly reduce the amount of salt residue. It is also possible to choose shrubs and trees that are less susceptible to the effects of salt. Trees such as white oak, catalpa and service berry and shrubs such as hydrangea, forsythia and witch-hazel, among others, can tolerate a higher level of salt.