Every winter, cities face a challenging trade-off: maintain safe roads and sidewalks with deicing salts, or protect the long-term health of urban trees and infrastructure. While road salt effectively keeps surfaces ice-free, its environmental impact—particularly tree damage—raises serious concerns for urban forest management.
UNDERSTANDING THE DAMAGE
Road salt’s effects on trees extend far beyond unsightly brown leaves. The salt interferes with trees’ fundamental processes, disrupting water and nutrient absorption while damaging young tissue. Late winter applications prove especially harmful, as there’s limited time for precipitation to flush the salt from root zones before spring growth begins.
Salt build-up also affects soil structure, creating poor drainage conditions that suffocate tree roots.
EFFECTIVE ALTERNATIVES AND MANAGEMENT
Several promising alternatives can reduce environmental impact while maintaining winter safety:
- Calcium magnesium acetate (CMA) and other calcium-based products cause less damage to the environment
- Proactive anti-icing liquids like beet juice and brine solutions can minimize overall salt usage
- Cost-effective sand and salt mixtures can be reused across multiple applications
Despite these alternatives, conventional rock salt remains dominant due to its affordability and reliability. To minimize impact, cities should:
- Train equipment operators in proper spreading techniques
- Apply materials sparingly where possible
- Avoid heaping snow around trees or in planting areas
- Prioritize alternative materials on roads with significant landscaping
SPECIES SELECTION AND SMART DESIGN
Landscape designers play a crucial role in minimizing salt damage through thoughtful planning:
“Strategically placed salt-tolerant trees can act as a barrier to protect less tolerant species from salt spray,” notes Coe Roberts, a certified arborist at the Arbor Day Foundation. Additional design strategies include:
- Avoid placing trees in low-lying areas or drainage collection points.
- Redirecting drainage or adjusting grade to protect vulnerable areas.
- Maximizing distance between trees and roadways where possible.
- Species selection is critical. While all trees are affected by salt, some species show remarkable resilience, others prove particularly vulnerable.
- Some salt-tolerant tree species include:
- Species particularly vulnerable to salt damage include:
- Red maples, Sugar maples, and Silver maples
- Littleleaf linden
- Basswood/American linden
- Pin oak
- Ironwood
- Hornbeam
- White pine
- European Mountain ash
- Eastern redbud
- Some salt-tolerant tree species include:
PROTECTIVE MAINTENANCE STRATEGIES
Arborists and maintenance teams can implement several effective measures:
Create physical barriers:
- Install snow fences or burlap screens for roadside trees
- Wrap young or vulnerable tree trunks in burlap during salting season
- Remove protective wrapping once salting ends
Soil management:
- Apply Mulch:
- thick layers around tree bases will slow salt seepage and insulate the roots.
- Add Gypsum (calcium sulfate)
- Gypsum displaces sodium ions with calcium ions, freeing the sodium from soil particles so it can be washed away. It also improves soil structure, leading to better drainage and aeration. Gypsum can also be applied as a preventative measure in the fall, before salting begins.
- Recommended rates vary between 9 and 18 kilos per 9 square metres of soil surface, depending upon salt content and soil texture.
- Flush with Water
- After temperatures warm and before spring growth begins, flush the soil with 6 inches (15 cm) of water, which will leach out approximately 50% of the soluble salts. This is a crucial step to correct saline soils.
- Replenish Nutrients:
- Fertilizer, Biochar, and compost can be incorporated into the soil.
- Leached potassium and magnesium can be replaced through application of fertilizer.
The challenge of balancing road safety with tree health isn’t going away, but neither is our ability to adapt and improve. Through better salt management, smart design choices, and proactive tree care, we can maintain both safe winter streets and thriving urban forests for generations to come.
Salt tolerant Honeylocust trees, planted in GreenBlue Urban’s ArborSystem, thriving in New York City.
