It is not known if fairy ring is started by the white, hair-like fungal mass known as a fungal mycellium or by germination of the fungal spore produced in mushrooms. Researchers have attempted to produce fairy ring under experimental conditions but have been unsuccessful. They have found however, that the fungus begins to grow in either the soil itself or in the thatch layer above the soil. Thatch is the accumulation of dead roots and shoots produced by the lawn. The fungus lives by decomposing organic matter and moves deeply into the soil forming a dense, thread-like network of white mycellium that penetrates the soil to a depth of 10 inches to 20 inches.
Some reports indicate that the fungal mass reaches as much as two feet.
The lush, dark green grass forming around the ring is caused by nitrogen released by the fungus as it decomposes the organic matter in the soil. The dark green is more pronounced if the surrounding lawn needs fertilizing. By contrast, the dead or dry zone is the result of insufficient moisture. The network of mycellium growing through the pores of the soil prevents water from reaching the plant's roots. Unfortunately there has been limited success treating fairy ring with fungicides and chemical wetting agents.