Road salt, primarily composed of sodium chloride, is widely used to keep roads and walkways clear during winter. This material functions by dissolving in water to create a brine solution, which effectively lowers the freezing point of water below 32°F (0°C). While this application is effective for public safety, the resulting salt runoff is highly detrimental to turfgrass. The damage is a consequence of chemical interference and physical dehydration, which severely disrupt the plant’s ability to survive and grow.
How Salt Damages Grass
The primary mechanism by which salt harms grass is through osmotic stress, often described as physiological drought. When the concentration of salt ions in the soil solution becomes higher than the concentration inside the grass roots, water is drawn out of the roots to balance the concentration gradient. This process, known as reverse osmosis, dehydrates the plant’s tissues, causing it to wilt and die of thirst even when the surrounding soil is saturated with snowmelt.
In addition to dehydration, the individual ions that make up the salt—sodium and chloride—are toxic to grass cells. Chloride ions are particularly damaging, as they are readily absorbed by the roots and travel up to the leaves where they accumulate to toxic levels. This buildup interferes with photosynthesis and other metabolic processes, leading to cell damage and the eventual death of the leaf tissue.
The presence of high levels of sodium ions also negatively impacts the soil structure and nutrient uptake. Sodium displaces other beneficial nutrients, such as potassium and calcium, from the soil particles, making them unavailable to the plant. Furthermore, excessive sodium can cause the soil’s clay particles to disperse, which leads to compaction and a reduction in drainage and aeration.
Recognizing Salt Injury
Salt injury often manifests with visual cues, typically appearing in the areas closest to salted surfaces. The most common symptom is the browning or “scorching” of the leaf tips and margins, which is a sign of ion toxicity damage. The turfgrass may also appear wilted, stunted, or thinned, indicating the onset of physiological drought.
Damage is most commonly observed in early spring as the grass attempts to break dormancy and begin new growth. Patches of turf fail to green up, remaining straw-colored and dead, often forming distinct strips along sidewalks, driveways, or roadsides where salt runoff concentrates. In severe cases, a white, crusty salt residue may be visible on the soil surface.
Comparing Common Deicing Salts
The term “road salt” encompasses several chemical compounds, and their potential to harm grass varies significantly. Sodium chloride is the most common and least expensive deicer, making it the most damaging due to its high toxicity to turfgrass. Calcium chloride and magnesium chloride are generally more effective at lower temperatures and are often considered slightly less toxic to plants than sodium chloride.
All chloride-based salts introduce the toxic chloride ion into the soil, which remains the primary cause of plant injury. Magnesium chloride has sometimes been shown to be the least harmful among the chloride group. Alternatives like Potassium Chloride can still cause serious injury and are not preferable to sodium chloride, despite being a plant nutrient.
Non-salt alternatives exist, such as Urea (a nitrogen-based fertilizer) and Calcium Magnesium Acetate (CMA). Urea is less corrosive and chloride-free, but it is less effective at very low temperatures and requires large amounts, which can lead to nitrogen runoff concerns. CMA is safer for plants and less corrosive, though it is significantly more expensive than rock salt.
Practical Steps for Protection and Recovery
Protecting grass from salt damage involves preemptive measures throughout the winter season.
Protection Measures
- Install physical barriers, such as burlap or snow fencing, before winter to shield vulnerable turf along walkways and roads from salt spray and runoff.
- Apply a layer of mulch or compost along the edges of concrete surfaces to help trap salt before it leaches into the root zone.
- When applying deicers, avoid over-application, as using more salt does not significantly speed up the melting process.
- After shoveling, direct the salt-laden snow piles away from grass areas to prevent a concentrated dose of salt from melting directly onto the turf.
- Utilizing safer, alternative deicers like CMA or abrasive materials such as sand can reduce the chemical load entering the soil.
Recovery Steps
If damage has already occurred, recovery in the spring centers on flushing the soil. Deep, consistent watering helps to leach the accumulated salt ions downward, past the plant’s root zone, reducing the toxic concentration. Following this leaching process, applying soil amendments like gypsum (calcium sulfate) can help counteract the effects of high sodium by improving soil structure and water penetration. Once the soil is repaired, dead grass should be raked away and the damaged areas should be reseeded, ideally with salt-tolerant varieties such as tall fescue.