As heavy winter snow melts away, you may discover large patches of your lawn that are matted down and appear straw-colored or gray. This is caused by gray snow mold, a fungus.
Cause of Snow Mold
Snow Mold occurs when snow or leaves cover lawns for a prolonged period through the winter, especially in shady areas. The mold forms a circular shape, and actively grows when temperatures are just above freezing. Heavy snow cover can actually insulate the ground and keep it from freezing, creating the perfect conditions for this fungus to thrive.
Snow Mold does not thrive in dry warm conditions, and typically the worst symptoms are that the affected patches will take slightly longer to green up in the spring than unaffected areas. Typical front range winters to not lend themselves to the growth of Snow Mold, as we rarely have heavy snow cover over extended periods of time. However, the occasional years when we do see a heavy blanket of snow that doesn’t quickly melt off lead to widespread Snow Mold in people’s lawns.
Treatment of Snow Mold
Chemical treatments are not recommended for the treatment of a lawn already affected by Snow Mold. To help your lawn recuperate for spring, gently rake the affected areas to knock away dead leaves and fluff up matted areas. This will help increase air flow and reduce the conditions that are favorable to mold growth. Do not power rake affected grass, as this can risk damaging and possibly destroying the already traumatized plants.
Prevention of Snow Mold
The best cure for Snow Mold is prevention. Thatch management is an important key in Snow Mold prevention. Practice core aeration of your lawn at least once a year to keep thatch levels below 1/2″. Another important factor is mowing the grass short before winter. Cut the lawn to 1-1/2 to 2” at the last mowing. This should be a gradual process and not a one-time exercise. Lower the height a notch a week until the mower is set at 1-1/2 to 2”. Remove leaves and matted materials from the lawn in the fall, which encourages proper air flow. Avoid heavy applications of nitrogen in the fall, as this can cause grass to push out new growth late in the season, adding to matting problems.
If Snow Mold is a consistent problem over several years, applying a fungicide, like F-Stop from Fertilome, in the fall can prevent damage. However, it should be noted that this is only effective as a preventative measure and should only be done when severe and repeated cases of Snow Mold have taken place.
Originally published on November 5th, 2010. Updated on April 30th, 2019.