Fairy Rings: Why Mushrooms Grow in Circles

One morning you look out at the lawn and there it is: a circle of mushrooms, or a ring of grass that’s greener than the rest. People once believed these circles were dance floors for fairies. Today we know they’re made by fungi, and the real explanation is almost as interesting as the folklore.

This guide explains how fairy rings form, the three types you might see in a lawn, which mushrooms are responsible, what to do about them, and why you should never assume the mushrooms in a ring are safe to eat.

What is a fairy ring?

BBC Wildlife Magazine defines a fairy ring as “a dark patch of grassy ground that produces a circle, or partial circle, of small mushrooms, usually in autumn.” Over the years the circles have also been called fairy courts, fairy walks, fairy grounds and hag tracks. According to the same article, people once believed the rings were dance floors for night-time fairies, with the mushrooms serving as seats.

Fairy rings can be small or very large. The Maine Department of Agriculture, Conservation and Forestry says they range “from a few inches to 200 feet in diameter.”

How do fairy rings form?

The mushrooms you see are only a small part of the fungus. Most of it lives underground as mycelium, a network of fine threads that spreads through the soil.

Mycologist Michael Kuo, writing on MushroomExpert.com, explains the basic pattern. When food in the soil is evenly spread, the mycelium grows outward in all directions from its starting point. If it produces mushrooms, they appear at the outer edge of the circle. BBC Wildlife compares this to apples on a tree: the mushrooms around the ring all belong to one organism.

Why a circle?

Montana State University Extension puts it simply: the ring shape comes from “the natural radial growth pattern that fungi exhibit.” Each year the ring expands. University of Nevada Cooperative Extension says rings spread outward from a central point at roughly 1 to 2 feet a year, and can “grow right out of a small lawn.”

Because the ring keeps expanding, a bigger ring generally means an older fungus. Kuo notes that some studies, which assumed the ring grew evenly each year, estimated that the mycelium of large rings could be “hundreds of years old!” That figure depends on the assumption of steady growth, so treat it as an estimate rather than a measured age.

How deep does the fungus go?

The Nevada fact sheet says the mycelium can reach 10 to 20 inches deep in loose soil, and pathologists have found it as deep as 4 feet. In clay soil, it may stay in the top 1 to 2 inches.

Why lawns?

Lawns are among the most common places to see fairy rings. Kuo explains that lawns are maintained to be even, which gives the mycelium a consistent environment to spread through. In woodland, soil is less uniform, so complete rings are less common, although he has seen mushrooms such as Amanita and Russula fruiting in large arcs.

The three types of fairy ring

University of Nevada Cooperative Extension describes three types of fairy ring in lawns. You may see more than one effect in the same ring.

Type	What you see	What causes it
Type I	Zones of dead grass, sometimes as two rings, often without mushrooms	Water-repellent fungal threads stop moisture reaching the roots, so the grass dies from drought
Type II	A ring of lush, dark green grass	Nitrogen released as the fungus breaks down organic matter
Type III	A ring of mushrooms, with no visible harm to the grass	The fungus fruiting at the edge of the ring

Why is the grass greener?

As the fungus breaks down dead roots, thatch and buried wood, it releases nutrients. The Nevada fact sheet points to nitrogen, and says Type II rings are most visible in spring before regular fertilising, and more noticeable in lawns that are short of nitrogen. Montana State University Extension says the “darker color in the grass is caused by excess nutrients”. BBC Wildlife adds that the fungus “liberates nutrients in the soil, enabling the vegetation at the edge of the circle to grow taller.”

Why does grass sometimes die?

In Type I rings, the problem is water. The Nevada fact sheet explains that dense, water-repellent mycelium can stop water soaking into the soil, so the grass above suffers drought even when the lawn is watered. In arid and semi-arid regions, it says, the effect can last 12 to 18 months.

“Fairy chemicals”: a surprising discovery

Fungi may affect grass in another way too. In a 2018 article for C&EN, published on the American Chemical Society’s Axial site, Louisa Dalton described the work of Hirokazu Kawagishi of Shizuoka University in Japan. Kawagishi noticed circles of darker, taller grass on his campus. Mushrooms appeared in the patches, and he isolated a growth-promoting molecule from the mushroom Lepista sordida.

The molecule is called 2-azahypoxanthine, or AHX. Kawagishi and colleagues named it and its close relatives “fairy chemicals”. According to the article:

Every crop tested, including rice, wheat, corn, tomatoes and tobacco, responded to AHX.
Field trials with AHX alone raised rice and wheat grain yields by 10 to 20%.
AHX “itself is rather unstable”, which limits how it can be used.

A 2015 study by Asai and colleagues in Japan Agricultural Research Quarterly tested AHX on rice in pots and fields. It found that AHX improved brown rice yields, with panicle number and stem length tending to increase, while grain weight was not affected.

This research is still at an early stage. The C&EN article notes that it can take a long time for the agricultural industry to vet a new molecule, so don’t expect fairy chemicals on garden centre shelves soon.

Which mushrooms make fairy rings?

Many different fungi can form rings. The Maine Department of Agriculture, Conservation and Forestry says about 50 to 60 species are known to form fairy rings in turf. Kuo goes further, suggesting that nearly any ground-dwelling mushroom can form a ring if the soil is even enough.

Mushroom	Notes from our sources
Marasmius oreades, the fairy ring champignon	The most common cause of lawn fairy rings, according to the Nevada, Montana and BBC Wildlife sources. BBC Wildlife describes it as common on lawns and playing fields.
Agaricus species	Listed by the Maine DACF and by Kuo as fairy ring formers
Puffballs (Lycoperdon species)	Listed by the Maine DACF
Earthballs (Scleroderma species)	Listed by the Maine DACF
Chlorophyllum molybdites, the green-spored parasol	Forms rings in lawns, according to Kuo and the University of Florida. Poisonous.
Lepista sordida	The source of the “fairy chemical” AHX

Our featured photo shows Marasmius oreades, the species field guides call “the fairy ring mushroom”. As Kuo points out, though, it “is not the only fairy ring mushroom.”

Are fairy ring mushrooms safe to eat?

Don’t assume so. A ring can be formed by an edible species, a poisonous one, or one you’ve never heard of. University of Nevada Cooperative Extension warns that many ring-forming species produce mushrooms that “may be toxic to humans and especially toxic to small children and pets.”

The green-spored parasol

One ring-former deserves special mention. The University of Florida describes Chlorophyllum molybdites, the green-spored parasol, as “the most common cause of mushroom poisoning in the United States”, citing a 1992 study. It “commonly creates a complete or incomplete ‘fairy ring'” in lawns and grassy areas.

According to the University of Florida fact sheet:

Symptoms such as nausea, vomiting and diarrhoea start 1 to 2 hours after eating.
Severe cases can involve bloody diarrhoea and shock from fluid loss.
Most patients recover within 24 hours, though symptoms can last from 4 hours to 7 days.
It can easily be confused with edible parasol mushrooms.
Its spore print is green, which the fact sheet calls “a rare feature among mushrooms.”

The safest approach is simple: don’t eat mushrooms from your lawn unless an experienced local expert has identified them. If a child or pet may have eaten one, contact a poison control centre or a vet straight away. Our guides to mushroom poisoning and poisonous mushrooms and dogs explain what to do. Photo apps can be a useful learning tool, but our review of mushroom identification apps explains why they shouldn’t decide what’s safe to eat.

Should you get rid of a fairy ring?

Often, you don’t need to. Montana State University Extension says fairy rings are usually not harmful to lawns, and no control is needed if you can live with slight colour differences. BBC Wildlife calls the fairy ring champignon harmless, though a problem if you need perfect turf.

If a ring is causing dead patches, extension services suggest these options:

Approach	What extension services say
Mask the ring	Fertilise the whole lawn so the rest greens up to match the ring (Nevada)
Mow, aerate and fertilise	Reduces differences in grass colour and health (Montana)
Water deeply	Keep the lawn from drying out and water to 6 to 8 inches deep (Nevada)
Break up the soil	Drilling, drenching or aerating can suppress the fungus, though it won’t eliminate it. Keeping the soil moist for 4 to 6 weeks helps (Nevada)
Remove and replace	Removing turf and repeatedly tilling the soil is effective, followed by reseeding (Nevada). Montana notes this is “not always effective”
Fungicides	Montana says they are “strongly discouraged because they are not very effective”. Nevada reports limited success

Removing the mushrooms

The Nevada fact sheet suggests removing mushrooms by hand or by mowing as soon as they appear, especially where children or pets play. Wear gloves if you’re handling unknown mushrooms, and wash your hands afterwards. Removing the mushrooms won’t remove the fungus underground, so they’re likely to come back.

Preventing new rings

The Nevada fact sheet suggests keeping the lawn from drying out, following fertiliser rates, aerating in spring or early autumn, and removing buried wood before planting. It notes that rings often appear in lawns that are underwatered and underfertilised, though they can develop in well-kept lawns too.

Fairy rings and the bigger picture

Fairy rings are a visible sign of something that happens out of sight in almost every patch of soil: fungi breaking down organic matter and recycling nutrients. Some fungi go further and partner with plant roots, as our article on the “wood wide web” explains.

The bottom line

A fairy ring is a fungus growing outward through the soil, often by 1 to 2 feet a year, with mushrooms or greener grass marking its edge. Around 50 to 60 species can form rings in lawns, with Marasmius oreades the most common. Most rings do little harm and can be masked with good lawn care. But some ring-forming mushrooms, including the green-spored parasol, are poisonous, so keep children and pets away and never eat lawn mushrooms without expert identification.

Sources and further reading

Featured image: fairy ring champignon by Ben Keen via iNaturalist (CC0 1.0).

Fairy Rings: Why Mushrooms Grow in Circles, and What to Do About Them

What is a fairy ring?