Ice rarely kills grass solely through freezing temperatures. Instead, prolonged ice cover triggers several distinct biological and physical mechanisms, collectively known as “winterkill.” These mechanisms include cellular rupture, suffocation (anoxia), and extreme dehydration. Understanding the specific science behind these processes helps explain why a lawn can emerge from a snowy winter with severe, patchy damage.
Physical Damage From Ice Cover
A thick, impermeable sheet of ice covering the turfgrass for an extended period can cause death primarily through suffocation, a condition known as anoxia. When ice encapsulates the grass plants, it forms an airtight barrier between the soil and the atmosphere, preventing the necessary exchange of gases. The living grass crowns and soil microbes continue to respire, consuming the limited oxygen trapped beneath the ice layer and releasing carbon dioxide.
As oxygen levels drop and carbon dioxide concentrations rise, the plants are forced into anaerobic respiration, a survival mechanism that produces harmful byproducts like organic acids and toxic alcohols. Research suggests that prolonged ice encasement, especially lasting more than 45 to 90 continuous days, can be lethal due to this toxic environment. While the physical weight of the ice can cause minor crushing, the suffocating effect of the ice sheet is the more destructive physical threat to the crown.
Cellular Stress and Winter Burn
Fluctuating temperatures in late winter often lead to complex cellular damage.
Crown Hydration
Crown hydration occurs when a mid-winter thaw allows the grass crown—the plant’s growing point located near the soil surface—to absorb excess water. When temperatures rapidly drop again, this internalized water freezes, expanding and rupturing the cells within the crown. Because the crown is the source of all new root and shoot growth, this cellular rupture is often fatal to the plant. Grasses that come out of dormancy too early during a warm spell are highly susceptible to crown hydration when the inevitable hard freeze returns. The result of this freeze-thaw cycle is a patch of dead grass that will not green up in the spring.
Winter Burn
The grass also faces a desiccation injury known as winter burn, which is death by drying. This occurs on cold, sunny, and windy days when the grass blades lose moisture through transpiration. Since the soil is frozen, the grass roots cannot take up water to replace the moisture lost from the leaves. This lack of available water leads to severe dehydration, essentially turning the grass into straw. Winter desiccation is most common in exposed, elevated areas where dry winds are strongest and where a protective layer of snow cover has not insulated the turf. Although the leaves are often the primary tissue affected, prolonged desiccation can eventually kill the entire crown.
How De-Icing Salts Affect Grass
Runoff from de-icing salts used on adjacent walkways and driveways is a major cause of localized winter damage. The most common de-icers, which contain sodium chloride or calcium chloride, are highly detrimental to turfgrass. When the salty meltwater permeates the soil, it creates a concentration gradient that draws moisture out of the grass roots.
This process is known as osmotic stress, and it dehydrates the plant cells, creating a condition similar to fertilizer burn or drought. Beyond dehydration, the chloride ions themselves are toxic, interfering with the plant’s metabolism and nutrient uptake. The damage often appears as a dead, brown strip of grass bordering the hard surface where the salt-laden water pooled and soaked into the soil.
Sodium chloride is particularly damaging because the sodium can degrade the soil structure, leading to compaction and poor drainage that further stresses the grass. Even products marketed as “lawn-safe” often contain chloride salts, and their overuse can still result in significant injury to the root zone.
Strategies for Lawn Recovery
The first step in recovery is preventing further damage by avoiding all foot traffic on frozen or ice-covered turf. Walking on frozen grass can crush the brittle, dormant crowns, and stepping on a thick ice sheet can compact the soil beneath. If an ice sheet is present, it should be broken up gently to allow for gas exchange, but only if the ice can be removed without physically tearing up the grass below.
In the spring, once the ground has thawed and temperatures are consistently above freezing, assess the damage by lightly raking affected areas to remove matted, dead debris. This step allows air and sunlight to reach the crowns of any surviving grass plants. For areas with severe loss, spring repair should focus on aeration and overseeding.
Aeration can relieve compaction and improve drainage, which helps flush out any residual salts from the soil. Overseeding the bare patches with a starter fertilizer promotes new growth, but this should only be done when soil temperatures are warm enough for germination. This temperature is typically above 50 degrees Fahrenheit for cool-season grasses. Watering the seeded areas regularly will ensure the new seedlings establish themselves and help the surviving turf recover its health.