Snow Mold is caused by a fungus that is active over the winter underneath the snow. Generally, snow mold will not kill your grass...it just looks bad.
Snow mold can be a sign of one or more of the following:
*We had a lot of snow cover this past winter
*Your lawn wasn’t mowed short enough last fall
*Your soil is wet and holding moisture
*Your soil lacks good biology to combat the fungi that causes snow mold
*You have a lot of problem grasses (like bentgrass or rough bluegrass) that are very susceptible to snow mold
There isn’t that much you can do about what’s already happened, but the good news is that the lawn will recover soon on its own. A little light raking will help speed the process...but don’t rake too aggressively because that can potentially kill the grass. If snow mold is really bothering you, ask us to do a Super Seeding for you, which will help the old grass recover and get new grass established.
To prevent snow mold next year, make sure you mow your lawn late into the season (with sharp blades) down to about 2 inches, (pretty short) so that the grass doesn't lay over on itself. Also, consider beneficial liquid aeration this fall to help open up the soil and encourage beneficial soil biology. A compost topdressing will also add snow mold fungi fighters.