Fairie rings, pixie rings, witches’ rings. These are some of the names associated with the odd-looking circular or semicircular fungal growths that occasionally appear in lawns. Folk lore tales regarding these growths range from the harmless (fairies and elves merrily dancing in a circle) to the sinister (pagan celebrations involving witches). But there’s nothing magical or sinister about these rings.  They are completely natural phenomena.
Fairy rings are commonly found in lawns that have a high level of organic matter, such as a buildup of thatch. Thatch is typically made up of dead and living grass clippings, stems and roots that form a layer between the soil and actively growing grass blades. While a little thatch is not a problem normally, too much thatch can prevent water, air and nutrients from reaching grass roots. This adds to stressful growing conditions for turf grasses and creates the perfect environment for fairy rings to develop.
Fairy rings generally occur in lawns and golf courses. Â They are also found in woodlands and in areas where trees have been cut down or removed leaving behind decomposing roots and stumps suitable for wood-rotting fungi species to consume.
WHAT IS A FAIRY RING?
A fairy ring is a circular or semicircular area of abnormal turf growth. It often occurs in turf grass that is suffering drought conditions or in soil that has low fertility.  When it first appears in the turf, the ring is small, measuring a foot or less in diameter. The fungus begins growing in the center of the ring and expands outward in a circular pattern that increases in size each year. Although the rings typically range from 2 to 15 feet in diameter, they can grow much larger. For example, according to the North Carolina State Extension’s TurfFiles, the size of a fairy ring can reach several hundred feet in diameter in old turf stands.
WHAT CAUSES A FAIRY RING?
Fairy rings are caused by a class of soil-dwelling fungi known as Basidiomycota (formerly referred to as basidiomycetes) and are sometimes referred to as “mushroom fungi.” The fungi don’t directly attack the grasses, but they can alter the soil chemistry, which indirectly affects turf. The fungi break down organic matter in the soil. The fungus puts out lots of small threads, or mycelia, which grow in a circular shape. According to the Missouri Botanical Garden website: “A fairy ring starts from a piece of mycelium or spore at a single point feeding in the thatch layer or on soil organic matter. The uniform outward growth of the fungus results in the development of rings.”
WHAT ARE SOME SIGNS OR SYMPTOMS OF A FAIRY RING?
At least 50 species of soil-inhabiting Basidiomycota fungi are associated with three different types of fairy rings in turf grasses. Â Depending on the type of fairy ring, the signs or symptoms can vary depending on the strain of fungi present in the soil and can include any of the following:
- A ring or arc of thin, dying or dead grass develops in the lawn.
- The soil within the ring tends to be drier than the soil surrounding the ring.
- The soil within the ring may contain an extensive network of white, thread-like fungal strands. It is this extensive fungal colonization that prevents water from permeating into the soil.
- The ring increases in size, becoming larger each year.
- The rings may be visible throughout the growing season but generally disappear once the turf goes dormant in fall or winter.
- In very dry or drought-like conditions, the fungus may not appear at all. Although not visible, the fungal spores remain in the soil waiting for the right circumstances to make an appearance in the turf.
- The ring may be dark green in color and faster growing than the surrounding turf.
- Under wetter conditions, fruiting bodies (mushrooms or puffballs) may suddenly appear along the outline of the fairy ring.
- If the ring develops on a slope, the bottom of the ring may be open, forming an arc.
An interesting observation about fairy rings is that two rings will not cross each other in the turf. According to the University of Maryland Extension publication on Fairy Rings – Lawns, “they may actually inhibit one another, which can disrupt the ring development.”
TYPES OF FAIRY RINGS
When confronted with a fairy ring in the lawn, it’s important to identify the type. Depending on the environmental conditions, soil conditions and the fungus involved, a fairy ring may appear as one of three types:
Type I – Circular or semicircular bands of grass that are either dead or badly damaged. This type is more commonly associated with grassy recreational areas, such as golf courses or putting greens, than with home lawns, but they can occur in both. The fungi responsible for the condition produces compounds that cause the soil and thatch to become hydrophobic (water repellent). This condition reduces the amount of water that can be absorbed in the soil resulting in drought-like conditions that cause the grass in the ring to turn brown and die. This can happen even if the surrounding, unaffected soil has sufficient moisture. Type I fairy rings typically occur during periods of hot, dry summer weather. Of the three types of fairy rings described here, Type I is the most damaging to turf.
Type II – Circles of fast growing, dark green grass. The fungus associated with this condition feeds on decaying organic matter in the soil. As the organic matter decays, it releases nitrogen and other nutrients that promote lush dark green growth. This band of dense green grass, which typically measures several inches wide, grows faster than the surrounding turf. These symptoms typically indicate turf that is deficient in nutrients (particularly nitrogen and iron) or is underwatered or both. Type II fairy rings can occur anytime between bud break in spring and the first killing frost in fall but are most commonly encountered in hot, dry summers.
Type III – Circles or semicircles of mushrooms or puffballs. This type of fairy ring consists of a circle or semicircle of mushrooms or puffballs (fruiting bodies) that emerges from the ground around the outer edge of a fairy ring but with no visible effect on the turf grass. Although a Type III fairy ring can occur any time during the growing season, it usually appears in the lawn late in summer or early in autumn particularly after periods of extended or heavy rainfall and in soil that is poorly drained. Type III fairy rings are the most common type found in home lawns.
In addition to these three common types of fairy rings, some members of the Basidiomycota class of fungi feed on decaying organic matter such as tree stumps, roots, leaves and other woody materials.
WHAT IS THE BEST WAY TO CONTROL FAIRY RINGS?
Typically, fairy rings don’t cause much, if any, harm to turf. However, they can remain in the soil for years and can disappear or reappear whenever conditions are suitable. They tend to be more of a cosmetic issue than a threat to the health of the lawn. If you don’t want them in your lawn, the most effective way to control them is to prevent them from developing in the first place.
- As a general management strategy, remove decaying organic matter such as dead tree roots, logs, fallen limbs, stumps, and even large amounts of buried leaves to prevent wood-rotting fungi from becoming established in the soil.
- Aerate the turf to allow more water, oxygen, and nutrients to reach turf roots.   Monitor moisture levels in the soil for extremes in moisture or dryness. While it is important to get enough water to the root zone, don’t over saturate the soil.
- Have a soil test done periodically to determine nutrient levels.
The course of treatment depends on the symptoms observed for each of the three types of fairy rings. For Type I fairy rings, aerate the turf to remove excess buildup of dead grass cuttings, stems and roots. Â Irrigate the dethatched turf to re-wet the soil beneath it. This may mean adding a wetting agent (surfactant) to help the water penetrate the soil.
For Type II fairy rings, a soil test can reveal what nutrients, if any, are lacking. Some sources recommend an application of nitrogen fertilizer or iron in the area surrounding the fairy ring to green up the area and camouflage the fairy ring.   Â
Type III fairy rings generally disappear on their own without any intervention. So, no action is needed unless you find the mushrooms or puffballs unsightly or annoying. If that is the case, simply knock the mushrooms or puff balls with a rake or hoe or mow over them with your lawnmower to remove them.
According to the Virginia Cooperative Extension’s publication on Managing Mushrooms in the Lawn, chemical fungicide applications are typically not recommended for controlling soil-borne fungi in the lawn. That’s because the soil-borne fungi are “almost impossible to control with even the most active fungicides….” Also, these treatments may be prohibitively expensive for the homeowner.  But if you do use them, follow the instructions on the label carefully.
ARE FAIRY RINGS HARMFUL?
Although harmless to the lawn itself, the mushroom and puffball fruiting bodies associated with Type III fairy rings may be poisonous to both humans and animals. Few homeowners are experts on edible versus poisonous mushroom varieties. So, in the interest of safety, do not collect and eat fairy ring mushrooms. As a further precaution, do not handle them with your bare hands or dispose of them in the garbage. Also, don’t put them in your compost pile.  If you have small children or pets, it’s important to remove the fruiting bodies from fairy rings promptly as soon as they become evident.
FEATURE PHOTO: Type III Fairy ring in turf. Photo Credit: William M. Brown Jr., Bugwood.org.
SOURCES
Managing Mushrooms in the Lawn, Virginia Cooperative Extension
Lawn Fertilization in Virginia, Virginia Cooperative Extension Publication 430-011
Lawn Mushrooms and Fairy Rings, Missouri Botanical Garden
Fairy Ring of Turfgrass – FSA7539, University of Arkansas
Fairy Rings — Lawns, University of Maryland Extension
Fairy Ring in Turf TurfFiles, North Carolina State University Extension