Signs of fairy ring include a dark green circle or arc of rapidly growing turfgrasses, sometimes lined with a band of dead grass. Occasionally, mushrooms or puffballs form along the ring. Fairy rings develop most commonly in spring and fall when there is excess moisture. However, the circle may be seen year-round.
Fairy rings can affect all types of turfgrass.
Soil-inhabiting fungi that feed on decaying organic matter, such as tree stumps, dead roots, or buried wood, cause fairy rings. As organic matter decomposes, the fungi release nitrogen, which causes the dark green color. The fungus may become so dense in the soil that moisture cannot penetrate through it. The grass may then die from lack of moisture or from a build-up of toxic substances.
Fairy rings are not easy to eliminate. The most effective method involves replacing the affected soil to a depth of 12 inches and to a few feet beyond the outside of the green ring. The usual approach, however, is to try to mask the green ring by proper turf fertilization and core aeration, and to remove the mushrooms with a lawnmower or rake. Often, control measures are not warranted, as the fairy ring will advance from 5 to 24 inches per year and eventually move off the lawn. It is more of a curiosity than a threat to the quality of the turf. Talk to your landscape professional about available chemical management options.