Garden Variety: Repeated use of salt-based ice melt can hurt plants
photo by: Journal-World File Photo
The Lawrence area has already experienced two winter precipitation events this year that have warranted the use of de-icers to keep roads and sidewalks safe for travelers. Although necessary in many instances, de-icers can be detrimental to plants, especially when used repeatedly over the course of a season. Use them with caution in the vicinity of desirable landscape and garden plants, or seek plant-safe alternatives.
Salt damages plants by absorbing water in the soil, thus preventing plants from using it. Salt absorption also interferes with photosynthesis. Salt applied to roads and sidewalks through the winter washes from hard surfaces into nearby soil where it accumulates. Snow plows, blowers, and overzealous shovelers may push, blow, spray and throw salt even further into the landscape.
Although street and road crews must put safety first, thoughtful choices on home sidewalks and driveways can make a difference to the health of plants growing nearby.
Physical removal of snow and ice with a shovel, snow blower, leaf blower or broom is the safest for plants. Untreated snow can even be piled around the base of plants or over low-growing plants to provide extra insulation and moisture. De-icers and other options should always be used as a second step or alternative when complete physical removal of snow and ice from walkways is unachievable.
Rock salt, or sodium chloride, used to be the most common and least expensive de-icer. It is the most harmful to plants of available de-icers and should be avoided on sidewalks and driveways. As retailers and consumers understand the risks associated with using it, alternatives have gained ground, including calcium chloride, magnesium chloride, potassium chloride and calcium magnesium acetate. Determine what chemical is contained in your preferred ice melt product by checking the label.
Calcium chloride and magnesium chloride are typically easy to find and only a little more expensive than rock salt. These two, plus potassium chloride, are safe for plants if used as recommended. Since de-icers are often overapplied, there is still potential for damage and should be used with caution.
Calcium magnesium acetate products are the safest of the deicing agents for plants and work at extreme low temperatures. They are unfortunately the most expensive, but still cheaper than replacing a portion of the landscape or garden that has died from salt damage.
Sand, ash and kitty litter are nonchemical alternatives. They make walkways safer by providing traction on top of packed snow and ice. Sand and kitty litter are generally inexpensive. A fireplace or stove may provide a free source of ash for your use. They have little effect on the soil, but they may need to be swept from hard surfaces after snow and ice have melted.
Another option is to try a traction mat, also called ice mats. These are widely available online and may be available through some local retailers. Traction mats are made from layered sisal fibers and latex and typically come in 10-foot lengths that are either 18 or 30 inches wide. Roll the mat out over packed snow or ice and use it as a walking surface. They are reasonably priced, considering they can be used over and over for years to come.
Do-it-yourselfers may opt to lay down strips of old carpet or something similar to provide a steadier surface over snow and ice.
Salt damage occurs after plants break dormancy in the spring and water uptake is affect. Expect salt damage that occurs this winter to manifest itself in 2019 and 2020. Look for browning and scorching on the side of the plant nearest the surface where salt was applied. Evergreens may turn completely brown on the affected side. For plants at high risk of salt damage where the salt has already been applied, judicious watering in the spring may help to flush excess salt from the soil.
Pines, maples, redbuds, arborvitaes, yews and boxwoods are among the most salt-sensitive tree and shrub species.
Urea is sometimes recommended as an alternative to de-icers. It is a fertilizer with high nitrogen content. Instead of burning plants from salt, urea burns plants with excess nitrogen when overapplied and may also contribute to nitrogen runoff issues in the spring. There are simply better options out there.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.