The caps are whitish with irregular patchy darker scales and may be up to 12 inches in diameter. The lower surface contains gills that change from white to gray-green as spores develop. Fairy ring mushrooms often develop in arcs or complete rings. Generally, they first appear as a cluster of mushrooms or stimulated grass. The rings enlarge each year from a few inches to several feet.
Some rings disappear for a year or more and then reappear.
Fairy rings may be produced by 50 or more species of soil-inhabiting fungi. The dark green grass is largely due to the increased amount of nitrogen that is made available to the grass roots by the fungus as it breaks down organic matter in the thatch and soil. The ring of brown or thin grass develops largely as a result of drought stress caused by the dense growth of fungal material. This weakened grass is more susceptible to environmental stresses, disease, and weed invasion. Fairy rings are usually most severe in light-textured, low fertility soils low in moisture.