The Impact of Salts on Plants and How to Reduce Plant Injury from Winter Salt Applications

Across the country, more than 22 million tons of road salt is used every year. In Massachusetts, the Department of Transportation (MassDOT) recommends one or more applications of salt at 240 lbs per lane mile after every snow fall to ensure the safety of those using the roadways.

The most commonly used salt for deicing roads is sodium chloride (rock salt) because it is inexpensive, effective and readily available. Despite the benefits of improving safety on roads, streets, sidewalks, driveways and parking lots, deicing salt can cause damage to landscape plants. Deicing salts can cause injury and contribute to the decline and death of landscape plants. However, an understanding of the impacts salts have on plants and salt application management strategies can help to protect plants or reduce plant injury due to salt.

How Salt Affects Plants

Salt damage occurs on plants when salt is deposited by spray from passing cars on stems and buds of deciduous woody plants and on stems, buds, leaves and needles of evergreen plants. Salt spray can cause salt burn on buds, leaves and small twigs. Salt spray can also cause damage by desiccating the bud scales, exposing tender tissues of the developing leaves and flowers. The unprotected developing leaves and flower buds dry out and are often killed by the cold winter wind. Many times, the damage is not evident until late winter or spring. Needle or leaf browning, bud death, and branch dieback on the side of the plant facing the road or sidewalk is a common sign of salt spray damage. Damage to deciduous plants is not seen until growth resumes in the spring.

Plants are also affected by dissolved salts in runoff water. Sodium and chloride ions separate when salts are dissolved in water. The dissolved sodium and chloride ions, in high concentrations, can displace other mineral nutrients in the soil. Plants then absorb the chlorine and sodium instead of needed plant nutrients such as potassium and phosphorus, leading to deficiencies. The chloride ions can be transported to the leaves where they interfere with photosynthesis and chlorophyll production. Chloride accumulation can reach toxic levels, causing leaf burn and die-back.

Rock salt also causes damage when salt laden snow is plowed or shoveled onto lawns and garden beds. Salts in the soil can absorb water. This results in less water being available for uptake by the plants, increasing water stress and root dehydration. This is referred to as physiological drought, which, if not corrected, can lead to reduced plant growth.

The displacement of other mineral nutrients by sodium ions can also affect soil quality. Compaction can increase while drainage and aeration decrease, generally resulting in reduced plant growth. Damage from salt in the soil can be delayed, with plant symptoms not appearing until summer or even years later. Symptoms may also become evident during periods of hot, dry weather.

The extent of damage can vary with plant type, type of salt, fresh water availability and volume, movement of runoff, and when salts are applied. De-icing salts without sodium are safer for plants than sodium chloride. Salts applied in late winter generally result in more damage than salts applied in early winter because there is a better chance the salt is leached away before active root growth in spring. The volume of fresh water applied to soils also impacts the amount of salts leached away, while rainfall can wash salt from leaves.

Common Symptoms of Salt Injury

• Damage mostly on the side of the plant facing the road or sidewalk
• Browning or discoloration of needles beginning at tips
• Bud damage or death
• Twig and stem dieback
• Delayed bud break
• Reduced or distorted leaf or stem growth
• Witches’ broom development (tufted and stunted appearance)
• Wilting during hot, dry conditions
• Reduced plant vigor
• Flower and fruit development delayed and/or smaller than normal
• Fewer and/or smaller leaves than normal
• Needle tip burn and marginal leaf burn
• Discolored foliage
• Nutrient deficiencies
• Early leaf drop or premature fall color

Management Strategies for Mitigating Salt Injury

Reduce salt use. Combine salt with other materials such as sand, sawdust, or cinders that can provide grittiness for traction. De-icing materials that use salts other than sodium chloride, including calcium chloride, magnesium chloride, potassium chloride, or calcium magnesium acetate (CMA) are more expensive but can reduce injury to plants.

Make applications carefully. Applications should be targeted at walkways and roadways, not landscape beds or lawns. The flow of salt-laden runoff water should be considered for when snow melts. Avoid planting in areas where runoff naturally flows. Leaching soils by watering heavily can help remove salts from well-drained soils. This is not possible with poorly draining soils. Improve drainage of poorly drained soils by adding organic matter. To determine if you have high salt buildup in the soil, send a soil sample to the UMass Soil and Plant Nutrient Testing Laboratory.

Protect plants with physical barriers such as burlap, plastic, or wood. Use salt tolerant plants in areas near roads, driveways, and sidewalks. Remember that salt tolerant does not mean injury free.

The following is a table of the reported salt tolerance of selected trees and shrubs. It is important to keep in mind when choosing plants considered “salt tolerant” that the degree of tolerance and extent of damage are dependent on many factors, with tolerance varying in plants within the same species. Tolerance can also vary depending on method of salt exposure (spray vs. soil). There are conflicting reports for salt tolerance of many species. Soil type and climate variability can result in differences in plant response between areas.

Tolerant – Intermediate Tolerance	common name	Type of Salt Tolerance
Deciduous Trees and Shrubs
Acer campestre	hedge maple	Spray
Aesculus hippocastanum	horsechestnut	Spray and soil
Betula papyrifera	paper birch	Spray
Gleditsia triacanthos var. inermis	thornless honeylocust	Spray and soil
Larix spp.	larch	Spray
Quercus alba	white oak	Soil
Quercus rubra	Northern red oak	Spray and soil
Rhus spp.	sumac	Spray and soil
Rosa rugosa	rugosa rose	Spray and soil
Ulmus hybrids	elm hybrids	Spray and soil
Evergreen Trees and Shrubs
Juniper spp.	juniper	Spray and soil
Picea glauca	white spruce	Spray and soil
Picea pungens/Picea pungens ‘Glauca’	Colorado spruce/ Colorado blue spruce	Spray and soil
Pinus mugo	Mugo pine	Spray and soil

Sensitive Plants	common name
Acer rubrum	red maple
Acer saccharum	sugar maple
Amelanchier spp.	serviceberry
Buxus sempervirens	common boxwood
Cornus sericea	red twig dogwood
Juglans nigra	black walnut
Picea abies	Norway spruce
Pinus strobus	Eastern white pine
Pseudotsuga menziesii	Douglas fir
Quercus palustris	pin oak
Tilia cordata	littleleaf linden
Tsuga canadensis	Eastern hemlock
Viburnum spp.	viburnum

The following sources also have lists of reported salt tolerance of some common landscape plants:

Soluble Salts in Soils and Plant Health

https://www.extension.purdue.edu/extmedia/id/id-412-w.pdf

http://plant-pest-advisory.rutgers.edu/impact-of-road-salt-on-adjacent-vegetation/

Literature Cited:

Beckerman, J. and B.R. Lerner. 2009. Salt Damage in Landscape Plants. Purdue Extension. Factsheet ID-412-W

Gould, Ann. 2013. Impact of Road Salt on Adjacent Vegetation. Rutgers Cooperative Extension. New Jersey Agricultural Experiment Station.

Hunter, G. 1980. Salt Injury to Roadside Plants. Cornell University Bulletin 169.

Johnson, G.R. and E. Sucoff. 1999. Minimizing de-icing salt injury to trees. University of Minnesota Extension.

MassDOT Highway Division.  2015. Winter Road treatment and snow removal 

Missouri Botanical Garden. Salt Injury. http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/environmental/salt.aspx

Smithsonian.com. January 6, 2014. What happens to all the salt we dump on the roads?