Fairy rings are a common phenomenon in lawns and grassy areas, presenting as a circular or semi-circular pattern of altered grass growth. These arcs or rings are not caused by a pathogen directly infecting the grass but are the visible sign of a fungus growing beneath the soil surface. Understanding these formations is the first step toward managing them, as the solution depends on how the fungus manifests itself. The fungi are saprophytic, meaning they derive nutrients by decomposing organic matter within the soil. This breakdown of subterranean material alters the soil conditions, leading to distinct visual symptoms.
The Fungal Mechanics of Growth
The visible ring is the outer edge of a much larger, invisible fungal organism called the mycelium, a network of fine, thread-like structures. This fungal body originates from a single point, often decaying organic debris deep beneath the turf, such as an old tree root or stump. The mycelium expands radially outward from this source, creating the characteristic circular shape.
As the mycelium grows, it secretes enzymes to break down organic matter. This decomposition releases nutrients, notably a surge of nitrogen, into the soil around the growing edge. This sudden nitrogen availability stimulates the surrounding grass, causing it to grow more vigorously and display a darker green color than the rest of the lawn.
Fungal growth can also produce hydrophobic compounds—waxy residues that coat soil particles and thatch. This creates a water-repellent layer, making it difficult for water to penetrate the soil and reach the grass roots. This subterranean change, combined with the fungus’s radial expansion, drives the progression and varying symptoms of a fairy ring.
Identifying the Three Types of Rings
Fairy rings are classified into three types based on the visual symptoms they produce on the turf. Proper identification of the type of ring is necessary before attempting any control measures. The appearance of a ring can change depending on environmental conditions, often becoming more pronounced during hot, dry weather.
Type I rings are the most damaging, characterized by a ring of dead, brown, or dying grass. This necrotic zone occurs because the dense mycelial mat makes the soil highly hydrophobic, preventing water absorption and leading to drought stress.
Type II rings are the most common, identified by a ring of lush, dark green, and fast-growing grass. This stimulation zone results from the nitrogen and other nutrients released by the fungus during decomposition. Type II rings may or may not feature mushrooms at their outer edge, and the grass inside the ring may appear thin or normal.
Type III rings are the least problematic and are characterized solely by a circle or arc of mushrooms or puffballs. There is typically no noticeable change in the color or growth of the surrounding grass. These fruiting bodies are the reproductive structures of the fungus and are most prevalent during periods of heavy rainfall.
Practical Strategies for Lawn Management
Management depends on the specific type of symptom present. For the less damaging Type II and Type III rings, cultural practices are often sufficient to mask the symptoms. For a Type II ring, applying nitrogen fertilizer to the surrounding lawn helps the rest of the turf match the dark green color of the ring, camouflaging the problem.
Type I rings, which involve a water-repellent layer, require aggressive physical intervention to re-wet the hydrophobic soil. The affected area should be heavily aerated, either by spiking or using a hollow-tine aerifier, to break up the dense mycelial mat and allow water penetration.
Following aeration, apply a soil wetting agent, or surfactant, to help water penetrate the waxy fungal residues. The area should then be hand-watered frequently and deeply to rehydrate the soil.
For Type III rings, the only necessary action is to physically remove the mushrooms, or fruiting bodies, by raking or picking them up. This prevents them from releasing spores and reduces the risk of the fungus spreading.
Fungicides are generally considered a last resort and are not typically effective as a curative treatment for Type I rings. For Type II rings, certain fungicides can be used, but they require deep penetration into the soil to reach the active mycelium. This usually involves drenching the area with water immediately after application.
The Origin of the Name
The unusual name “fairy ring” has roots in European folklore dating back centuries. Before the scientific understanding of fungi, people developed various supernatural explanations for their sudden appearance. The most common belief, particularly in English and Celtic traditions, was that the rings resulted from elves or fairies dancing in a circle during the night.
Other European cultures held different interpretations. In German folklore, they were sometimes called “witches’ rings” and were believed to mark the spot where witches danced. Austrian mythology attributed the circles to the fiery tails of dragons that had rested on the ground.