A fairy circle, also known as a fairy ring, is a naturally occurring circular patch of fungi or discolored turf found in lawns and grassy areas. This phenomenon is caused by a fungal colony growing beneath the soil surface, expanding radially outward. The name originates from European folklore, where these mysterious rings were once thought to mark the spots where fairies danced. The circle’s formation represents the visible edge of an unseen fungal network.
Identifying the Visible Signs
The presence of a fairy circle is identified by one of two distinct visual manifestations on the lawn’s surface. The most obvious sign is the sudden appearance of a ring of fruiting bodies, such as mushrooms or puffballs, common after periods of high moisture. These rings, often referred to as Type 3 fairy rings, can range in size from a few inches to many feet in diameter and are the reproductive structures of the fungus.
The second type of visual sign involves the grass itself, which can appear either unusually dark green and lush or brown and dead. A ring of dark green, fast-growing grass, known as a Type 2 fairy ring, is caused by nitrogen release from the fungus as it breaks down organic matter. Conversely, a ring of brown, dying grass, or a Type 1 fairy ring, results from severe water stress caused by the fungus. The specific appearance depends on the fungal species involved and the ring’s current stage of development.
The Fungal Network Behind the Ring
The visible signs are the perimeter of a much larger, underground structure called the mycelium, the main body of the fungus. A fairy circle begins when a single fungal spore lands and germinates in a favorable spot, typically where there is buried organic matter like old tree roots or stumps. The mycelium then grows outward uniformly in all directions, creating an ever-widening circle of microscopic, thread-like filaments called hyphae.
Radial Growth and Nutrient Release
This radial growth pattern means the ring expands in diameter each year, sometimes by several inches to a foot. As the fungus digests organic matter, it releases nitrogen compounds into the surrounding soil, which acts as a fertilizer. This causes the initial, dark green, lush ring of grass (Type 2). A common causative agent is the fungus Marasmius oreades, often called the Fairy Ring Mushroom.
Hydrophobicity and Damage
In older or more aggressive rings, the mycelial mat becomes incredibly dense and water-repellent, a condition known as hydrophobicity. This dense, waxy layer prevents water from penetrating the soil. This leads to the severe drought stress that causes the grass within or just inside the ring to turn brown and die (Type 1).
Options for Lawn Management
Addressing fairy circles focuses on mitigating the visual symptoms and improving water penetration. For a Type 3 ring, where only mushrooms are present, physically removing the fruiting bodies provides a temporary, cosmetic solution. Gloves should be worn, as some mushrooms can be poisonous. This action does not kill the underlying mycelium, which will continue to produce more mushrooms when conditions are right.
For rings causing turf damage or significant discoloration, the strategy is to disrupt the dense fungal mat and alleviate hydrophobic soil conditions. Core aeration, which involves punching holes into the soil, helps to physically break up the mycelium and improve drainage. Following aeration, a wetting agent can be applied to help water soak past the waxy fungal layer and reach the grass roots.
Deep watering the affected area repeatedly for several weeks is necessary to rehydrate the soil and dilute any potential fungal toxins. In cases of severe turf death, the most definitive solution is to completely remove the affected soil to a depth of about a foot and several feet beyond the visible ring. This soil must then be replaced with fresh soil, followed by reseeding or resodding the area. Since the mycelium extends deep into the soil, complete eradication is often difficult; maintaining a healthy, well-fertilized lawn is the best long-term preventative measure.