Fairy ring usually appears in the lawn as circles or arcs of dark green, lush, fast growing grass. These rings are most commonly between 2 and 15 feet in diameter. Since a fungus causes fairy ring you may see mushrooms, puffballs or toadstools in wet conditions in this same ring pattern. In some cases, a ring of brown or dead grass may appear.
The fungus is breaking down organic matter in the soil and producing amble nitrogen for the growing grass to use. The fairy ring fungus does not attack the grass itself. If the grass is brown or dead this is because the fungus is very dense and slowing water movement in the soil.
Typically fairy ring occurs where there are old tree stumps, roots, logs, lumber, and other larger pieces of organic material in the soil below the lawn. The fungus works to decompose these materials. Once the material is gone, the fairy ring will disappear. This may take a very long time.
Several fairy rings may appear relatively close together, especially on lawns that exist on sites that were previously wooded areas. You will notice that the rings do not cross each other and will appear broken. This is because fungus activity stops when fungi from different rings touch each other.
There are several options for managing fairy ring. Start at the lawn establishment stage by removing tree stumps and large roots, construction lumber, and such 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 growth strands (mycelia) from the fungi 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. In other words, put more fertilizer on the other grass so it will grow more and look like the fairy ring grass. Lawns watered and fertilized on a regular basis tend to have fewer problems with fairy ring.
Remember that most fungi are poisonous if eaten. If children or pets are a concern, break or mow off the mushrooms when they first appear. Touching the dark green grass is not a safety concern.
Go for a walk and look for fairy rings in your neighborhood. It might be fun to pretend fairies actually live there!