Snow is a natural part of the dormant season for turfgrass, presenting a complex balance of benefits and risks. The outcome depends entirely on the snow’s duration, temperature fluctuations, and the presence of a solid ice layer. A fresh, light blanket of snow is generally protective, but prolonged, wet, or compacted snow can create conditions that lead to severe winter damage. Understanding these dynamics ensures your lawn survives the cold season and greens up successfully in the spring.
The Protective Role of Snow Cover
A layer of snow functions as a natural insulator, shielding dormant turfgrass from damaging winter weather. This insulation is due to the high volume of trapped air within the snow’s crystalline structure, which acts as a barrier against rapid temperature drops. Even a modest blanket of snow can maintain the soil temperature near the grass crown at a stable level, often close to 32°F (0°C). This consistent warmth protects the grass crowns from dangerously low temperatures and freeze-thaw cycles that can cause cell damage. Without snow cover, turf is exposed to drying, cold winter winds, which can lead to desiccation injury. Melting snow also provides a steady source of moisture to the soil, helping to prevent the turf from drying out.
Potential Winter Damage to Turfgrass
While snow offers insulation, prolonged presence or mixing with ice can create environments conducive to turfgrass injury and disease. Severe damage is often observed in the spring when the snow melts to reveal large, damaged patches.
Snow Mold
One of the most common issues is the development of snow mold, a fungal disease that thrives in the cool, moist, low-oxygen conditions trapped beneath snow cover. There are two primary types: gray snow mold (caused by Typhula species) and pink snow mold (caused by Microdochium nivale). Gray snow mold typically only damages the grass blades, allowing the plant to recover in the spring. Pink snow mold is more damaging because the fungus can attack the grass crown and roots, potentially killing the plant. This disease is exacerbated when heavy snow falls onto unfrozen ground or on top of long, matted grass and debris.
Ice Smothering (Anoxia)
A solid, impermeable layer of ice can form, especially in low-lying or poorly drained areas, which is a major threat to turf health. Even when dormant, grass roots and crowns continue to respire, consuming oxygen and releasing carbon dioxide. A thick sheet of ice prevents this necessary gas exchange, leading to anoxic conditions that essentially suffocate the plant. The duration of the ice cover is the main factor, with some turfgrass species, like annual bluegrass, showing severe damage after 45 to 60 days under solid ice.
Crown Hydration/Freeze-Thaw Cycles
Crown hydration is often cited as the most destructive type of non-disease winter damage, typically occurring in late winter or early spring. It results from periods of thawing where the grass crowns absorb water, followed by a rapid drop in temperature that causes the water inside the plant’s cells to freeze. The expansion of ice crystals physically ruptures the cell walls, resulting in plant death. This damage is prevalent in areas with poor drainage where melting snow or rain collects and saturates the turf before a sudden overnight freeze.
Essential Pre-Winter Lawn Preparation
Mitigating the risks associated with snow and ice begins with proactive steps taken in the fall before the first permanent snowfall.
Adjusting your mowing height is one of the most effective preventative measures against snow mold. The final cut of the season should leave the grass blades at a height of approximately 2 to 2.5 inches. Grass left too long is prone to matting under the snow, which creates the humid, low-oxygen environment favored by snow mold fungi.
Core aeration involves removing small plugs of soil to improve gas exchange and reduce soil compaction. This practice enhances surface drainage, which reduces the risk of water pooling and subsequent crown hydration or ice smothering damage.
A late-season application of a “winterizer” fertilizer, often high in potassium and low in nitrogen, should be applied before the ground freezes. This application helps the grass store carbohydrates in its roots and crown, strengthening the plant’s cold hardiness and resilience against winter stress.