Q. We’ve noticed several wide, very green circles in the grass in our front lawn. Mushrooms are growing out of part of the circles. What are the rings and how do we get rid of the mushrooms?
A. The lawn grass circles you see are referred to as “fairy rings.” They are diseased areas characterized by lush, fast-growing grass growing in circles or arcs with mushrooms growing around the outside of the ring, particularly during wet, cool periods. They are called fairy rings because centuries ago, people thought mushrooms grew where fairies had danced the night before.
Fairy rings often appear where trees have been removed and stumps or roots have been left in the ground to decompose. The disease is caused by fungi feeding off of decomposing organic matter below ground; they are not feeding upon the grass. Nitrogen is one of the products of the decomposition process, which is utilized by the growing grass, causing dark green circles. Mushrooms are fruiting bodies of fungi that grow belowground.
The rings generally occur each growing season, especially if weather conditions are wet and cool or if the lawn is over-watered. During drought, fungal production may cease. The fungus producing the ring may live 8 inches or more below ground. In addition, the soil within the ring can become compacted as the fungus continues to grow underground. There is no easy remedy for controlling fairy rings. Fungicides are not effective; nor are home remedies.
The best option is to prevent fairy rings from occurring. Before establishing a new lawn, be sure that obvious roots, stumps, and pieces of construction lumber are entirely removed from the planting area. Exercise healthy lawn practices such as deep watering, core aeration, and dethatching when necessary. Fertilize only as needed and avoid excessive amounts of nitrogen. Rake and remove the mushrooms as needed.