Fairy ring may appear various ways in lawns. Circles or arcs of dark green, lush, fast growing grass is perhaps the most common, especially in spring. These rings are most commonly between 2 and 15 feet in diameter; although they may appear larger or smaller. Mushrooms or puffballs may appear under wet conditions in this same ring pattern. In some cases, a ring of brown or dead grass may appear.
Fairy ring fungi are not attacking the grass directly, but are breaking down organic matter in the soil. As a result, nitrogen is released that the grass above may use, causing the green ring. In cases where the mycelia of the fungus get dense and inhibit water movement into the soil, grass in the arc may turn brown. Mycelia may also deplete soil nutrients and produce toxic levels of hydrogen cyanide. The mushrooms that appear after rainfall are the fruiting bodies of the fungus.
The organic matter fairy ring breaks down is often old tree stumps, roots, logs, lumber, and other larger pieces of organic material in the soil below the lawn. Once this material is depleted, the fairy ring will disappear. This may take considerable time. Several fairy rings may appear relatively close together, especially on lawns that exist on sites that were previously wooded areas. When this occurs, it becomes noticeable that fairy rings do not cross each other, as fungus activity ceases when fungi from different rings contact each other.
There are several options for managing fairy ring. Start at the lawn establishment stage by removing tree stumps, large roots, and construction lumber prior to planting the lawn. When renovating a turf area that previously had fairy ring, be sure to blend all soil together, as different fairy ring fungi will attack each other. If several rings are visible at the time of renovation, collect the white mycelia from each and mix it together, then spread over the soil and work it in.
Fairy ring appearing as green arcs in established lawns can be masked somewhat by increased watering and fertilizing of the grass, keeping within suggested lawn care guidelines. Lawns watered and fertilized on a regular basis tend to have fewer problems with fairy ring. In addition, large quantities of water may be pumped into the soil in and around the rings using a root-feeder attachment to a garden hose.
Mushrooms and puffballs not associated with fairy ring may also appear in lawns, especially after heavy rains. As mentioned above, these are feeding on organic matter in the soil. Some may have a foul odor, some may be poisonous. As with fairy ring, eventually the food source will be depleted.
If many mushrooms appear in an area, dig up and remove the buried organic matter. If children or pets contacting the mushrooms are a concern, break or mow off the mushrooms when they first appear.