What mushrooms in your lawn may be telling you about moisture, drainage, and the hidden conditions beneath your grass You walk outside after several days of rain and notice something that wasn't there last week. Small mushrooms are scattered across the lawn. Maybe there are only a few. Maybe an entire patch seems to have appeared overnight. For many homeowners on Martha's Vineyard and Cape Cod, the first reaction is concern. Is the lawn sick? Is something damaging the grass?