Snow mold is a common lawn disease that emerges as winter snow cover begins to melt, causing alarm for homeowners observing matted, discolored patches. This fungal condition thrives in cool, moist environments, especially where grass remains compressed beneath persistent snowbanks or in poorly draining areas. Understanding the nature of this affliction is the first step toward effective lawn recovery and preventative measures.
Identifying Gray and Pink Snow Mold
Two distinct types of fungi are responsible for snow mold, each presenting different visual cues and levels of threat. Gray snow mold, caused by Typhula species, typically appears as circular patches ranging from a few inches to several feet across. These patches often have a grayish-white, cottony fungal growth (mycelium) visible at the edges. A characteristic of this type is the presence of sclerotia, which are small, hard, dark resting bodies embedded within the affected leaf tissue.
Pink snow mold (Microdochium nivale) often shows a pinkish-white margin when actively growing, especially just above freezing. Its mycelium may appear more web-like and less dense than the gray form. Unlike gray snow mold, pink snow mold can develop without snow cover, appearing in cool, wet conditions throughout the fall and spring. This distinction is important: Typhula generally limits damage to the grass blades, but Microdochium poses a greater risk to the plant’s survival.
Does Snow Mold Really Kill the Grass
Whether snow mold kills grass depends on the specific type of fungus and the duration of the infection. In most cases involving Gray Snow Mold (Typhula blight), the fungus only consumes the leaf blades, which are the non-growing portions of the plant. The crown, the actual growing point near the soil surface, is left undamaged and remains viable. As the lawn dries out and temperatures increase, the grass pushes out new shoots from the unaffected crown, leading to natural recovery. This process relies on air circulation and sunlight reaching the turf.
The matted, damaged blades will eventually decompose or can be removed, allowing the healthy turf underneath to re-establish itself. Recovery from Gray Snow Mold is often complete within a few weeks of consistent warm, dry weather. The threat to lawn survival comes specifically from Pink Snow Mold (Microdochium nivale), which can penetrate deeper into the turf structure.
Pink snow mold can directly attack and kill the crown of the grass plant, especially when conditions remain wet and cool for extended periods. If the crown is compromised, the plant cannot regenerate new blades, resulting in permanent dead spots. If the affected area remains brown or straw-colored after a week of favorable drying conditions, the grass likely needs reseeding. Areas affected by this crown-killing infection require direct intervention to restore turf density.
Stopping Snow Mold Before Winter Arrives
Preventing snow mold is more effective than treating the damage, starting with preparations in the late fall. Adjusting the final mowing height to approximately two to three inches is a simple preventative measure. Leaving the grass too long creates a dense, matted layer under the snow, trapping moisture and encouraging fungal growth.
Removing all organic debris, such as fallen leaves and clipped grass, from the lawn surface reduces the risk of infection. These materials insulate the ground and prevent the turf from drying out during brief winter thaws, allowing the fungus to spread. Cutting back any tall ornamental grasses that might fall over and mat the turf also prevents localized, high-moisture zones that promote fungal development.
Homeowners should avoid applying high-nitrogen fertilizers late in the growing season, typically after early September in northern climates. Nitrogen promotes lush, susceptible growth just before dormancy, making the tissue more vulnerable to fungal attack. Managing snow accumulation by avoiding large, dense snow piles from shoveling or plowing helps the underlying turf thaw and dry out faster in the spring, reducing the duration of favorable mold conditions.
Repairing Lawn Damage After Snow Melt
Once the snow has fully melted and the patches of mold are visible, the priority is to break up the matted grass to encourage air circulation and drying. A gentle raking or sweeping motion with a leaf rake is usually sufficient to lift the affected blades and disrupt the fungal mycelium. This action helps the soil surface dry, which is the most effective way to halt the mold’s activity and encourage healthy grass crowns to begin new growth.
The next step involves assessing the severity of the damage to determine where the crown is dead, particularly in areas showing signs of Pink Snow Mold. If the patches remain entirely brown and fail to show greening after the turf has dried out for a week, those spots require intervention. The dead turf should be lightly scarified before applying new seed or patching with sod to re-establish the grass cover.
While the ground is thawing and drying, avoid excessive watering, as the soil is already saturated from melting snow and winter precipitation. Fungicide applications are rarely recommended for spring recovery because cultural practices are effective once the weather warms and the ground dries. In lawns with a history of severe, recurring infection, however, a preventative fungicide application in late fall may be warranted.