BRIAN PAIGE
RECEIVES
BEACON AWARD
BRIAN PAIGE
Salt
RECEIVES
Damage
BEACON AWARD
Salt Damage to Woody Plants
Nicholas J. Brazee, UMass Extension Plant Pathologist
Damage to woody plants from exposure to de-icing salts can be a major concern during the winter season in New England. The injury to trees and shrubs occurs two possible ways, either as salt spray to the canopy or through root uptake of salts in the soil. Symptoms of salt damage vary considerably depending on the plant, distance from a treated surface, type of exposure( spray or root uptake), amount of salt applied, and soil type, among other factors. These symptoms can include: reduced vigor, stunted and / or deformed growth, marginal leaf / needle browning, shoot dieback, witches’ brooming and even outright death of the plant.
There is considerable variation in the susceptibility of both deciduous and coniferous plants to damage from de-icing salts, even within the same genus. For example, it’ s well known that eastern white pine( Pinus strobus) is very sensitive to salt damage, whereas pitch pine( P. rigida) is very tolerant of salts. Meanwhile, sugar maple( Acer saccharum) is also very sensitive to salt damage in urban environments, yet honeylocust tolerates salt exposure. Unfortunately, sensitivity to salt damage is often a major determining factor for municipalities when selecting tree species for urban planting.
The damage that woody plants experience from deicing salts is caused by chloride and sodium as these ions accumulate in stems and leaves. High levels of chloride negatively affect a variety of important processes and structures at the cellular level, such as inhibiting nitrate and phosphate uptake, damaging cell membranes and disrupting enzyme function. Plants respond to excess salts by translocating chloride and sodium ions to shoot tips and leaf margins, where they accumulate and symptoms manifest. In addition to causing damage directly to plant tissues, excess sodium in the soil raises soil pH and can make essential nutrients, such as calcium, magnesium, and iron, unavailable for root uptake. Chloride and sodium can leach from soils in certain settings, but they can also build up over time with repeated, annual applications.
A variety of de-icing salts are available for commercial and residential use, and it can be challenging to determine which is best when it comes to plant health. Two common forms, both used by the Massachusetts Department of Transportation, include rock salt( sodium chloride) and magnesium chloride. While highly effective, both are harmful to plants when taken up either as salt spray or through root uptake in the soil. Liquid brine, which is used to prevent ice from forming over treated surfaces, is created by mixing water with rock salt or a combination of salts( i. e. rock salt and magnesium chloride). Alternatives, such as calcium chloride and calcium magnesium acetate( CMA), are also effective and widely available. While both calcium chloride and CMA are believed to be less harmful to plants in comparison to rock salt and magnesium chloride, the results of various research trials do not always support this assertion.
In a study of the short and long-term effects of salts on silver maple( Acer saccharinum), Patykowski et al. found that calcium chloride was less toxic compared to sodium chloride, but when applied at high doses, both were equally as harmful. In comparative greenhouse trials, it was concluded that CMA is less harmful to herbaceous plants when evaluated against traditional de-icing salts. But in contrast, a study using potted tree saplings showed that CMA is equally as harmful to trees during vegetative growth when compared to sodium chloride. In addition, the high cost of CMA prevents its widespread use by many municipalities. Overall, it may be possible to limit plant damage by avoiding the use of rock salt and magnesium chloride, but only when low amounts of other de-icing salts are used. According to Sinclair:“ Salt absorption and subsequent damage increase with the amount of salt deposited on a plant. The type of salt is relatively unimportant.”
Therefore, to prevent salt damage from developing, limiting the amount used is likely the most important factor. To that end, restrict de-icing salt application to essential areas only and include sand when possible. Keeping plants well-watered during the spring season, if dry weather persists, can help to dilute salts that may be present in the soil. Manipulating soil grade or altering downspout drainage adjacent to sidewalks or driveways prone to ice formation may help to limit salt application in residential and commercial settings. However, in some landscapes, salt damage may be unavoidable given the needs to prevent and remove ice.
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MALP Newsline | Spring 2025 17