Mushrooms sprout in lawns after prolonged periods of wet weather, often in areas where dead organic matter has accumulated. Old tree roots, stumps or home construction debris, especially sawdust, encourage their growth.
Mushrooms may grow in a circle around grass, forming “fairy rings.” Grass inside these rings can be a darker green and grow more quickly. In some cases, there are so many mushrooms in these rings water can not penetrate into the soil and the grass dries out, sometimes dying. This leaves a ring of dead, brown grass and another ring of darker green, healthy grass.
Fungicides don’t usually kill fairy ring mushrooms in this region. Spring and fall aeration and several applications of a few ounces of dish washing solution in a gallon of water on the ring will sometimes make the ring less noticeable.
While there are many fungi that cause fairy rings, the presence of mushrooms in the lawn does not mean fairy rings will form. Most mushrooms that grow in lawns are feeding on dead organic matter which has accumulated in the lawn. The mushrooms can be mowed off or removed with a rake.
Lawn mushrooms may be poisonous or may cause allergic reactions and should not be eaten by humans or pets unless proper identification shows they are edible.
For “Lawn aeration” refer to message number 1505.
For more information, see the following Colorado State University Extension fact sheet(s).