Fairy rings are a common lawn problem that manifest as circular or semi-circular patterns of abnormal grass growth or bare patches. These rings are the visible sign of an underground fungal colony, specifically the mycelial growth of Basidiomycota fungi. Homeowners find these formations frustrating because they cause significant aesthetic damage and can result in localized patches of dead grass. The fungi feed on decaying organic matter beneath the surface, and while they do not directly infect the grass, their growth indirectly harms the turf.
Identifying the Types and Causes of Fairy Rings
Fairy rings are caused by various species of soil-dwelling fungi that decompose organic material like old tree roots, buried lumber, or excessive thatch. The fungi grow outward from a central point, forming a vast network of microscopic threads called mycelium beneath the soil surface. This outward expansion creates the ring shape observed in the lawn.
The visible symptoms are categorized into three main types based on how the fungus affects the grass. Type 1 is the most destructive, where the fungal growth produces a hydrophobic residue that coats the soil particles, making the area water-repellent. This localized drought causes the grass in the ring to die, leaving brown, wilted turf.
Type 2 fairy rings appear as a dark green, lush ring of grass that grows faster than the surrounding lawn. This results from the fungi releasing nitrogen and other nutrients into the soil, essentially fertilizing the grass at the ring’s edge. Type 3 fairy rings are the simplest form, characterized only by the appearance of mushrooms or puffballs, which are the temporary fruiting bodies of the fungus, typically emerging after heavy rain.
Aggressive Treatment Methods
For immediate and permanent elimination of a fairy ring, especially the highly damaging Type 1, the most aggressive method is physical excavation. This involves completely digging out the fungal colony and the soil in which it resides. The infected area must be removed to a depth of at least 12 to 18 inches and extended 1 to 2 feet beyond the visible edge of the ring to ensure all mycelial growth is captured.
After removal, the excavated area should be backfilled with fresh, sterile topsoil before reseeding or resodding. While this method is highly successful, it is labor-intensive and often impractical for very large or numerous rings.
Chemical control offers a less disruptive approach, utilizing commercial fungicides specifically labeled for fairy ring management in turf. These fungicides often belong to the DMI (Demethylation Inhibitor) or Strobilurin chemical families. For the chemical to be effective, it must penetrate the hydrophobic mycelial mat and reach the fungus in the soil, requiring application with a high volume of water, such as 2 gallons per 1,000 square feet.
To enhance penetration, the fungicide must be tank-mixed with a soil-wetting agent or surfactant. The entire area should be irrigated immediately after application to move the chemical deep into the root zone. Another aggressive chemical strategy involves the heavy application of a fast-release nitrogen fertilizer to rapidly accelerate the decomposition of the underlying organic food source, thereby starving the colony.
Cultural and Preventative Maintenance
Long-term management of fairy rings focuses on creating a soil environment hostile to the fungi and mitigating the hydrophobic effects of existing colonies. To combat the water-repellent layer of a Type 1 ring, mechanical aeration is necessary. Use a core aerator or garden fork to create deep holes, physically breaking through the dense fungal mat, which allows water and air to move into the soil.
Following aeration, the area must be repeatedly drenched with water to re-wet the dry soil. A soil wetting agent, or surfactant, should be applied to reduce the surface tension of the water and help it penetrate the hydrophobic fungal residues. This process should be repeated until the soil remains consistently moist, allowing the affected grass to recover from drought stress.
Preventing future outbreaks centers on improving overall turf health and eliminating the fungal food source. Before establishing a new lawn, all organic debris, such as buried construction materials, tree stumps, and large roots, should be completely removed from the soil.
Maintaining a healthy lawn involves diligent thatch control through regular dethatching or vertical mowing, as excessive thatch provides an ideal habitat for the fungi. Balanced nutrient management promotes uniform turf growth, making Type 2 rings less noticeable.
Consistent, deep, and infrequent watering encourages a deep root system and avoids stressed turf conditions that favor fungal colonization. Regular core aeration prevents soil compaction and thatch buildup.