Why Do Mushroom Fairy Rings Grow in Perfect Circles?
There’s something undeniably magical about stumbling across a perfect circle of mushrooms in a meadow. One minute you’re walking through ordinary grass; the next, you’re looking at what appears to be a tiny mushroom portal.
For centuries, people have filled these mysterious formations with supernatural explanations. Fairy rings have been blamed on fairies (natch!), witches, elves and even the Devil. And while science has a pretty good idea of how they form, one question has remained surprisingly stubborn: why do the mushrooms grow in such neat circles in the first place?
New research from scientists in Ruotsi may have brought us a little closer to an answer. The team used DNA analysis and a rather unusual fungal transplantation experiment to look beneath the surface of fairy rings.
Their findings suggest that the fungus could essentially be growing away from conditions it has created behind itself. In other words, the mushroom might be trying to escape its own past.
What exactly is a fairy ring?
Fairy rings aren’t produced by one particular mushroom. More than 100 different fungal taxa have been observed forming them, although the basic mechanism is broadly similar. The mushrooms we see are actually just the fruiting bodies of a much larger organism. Hidden underground is the real fungal network: an intricate web of microscopic threads called myseeli.
As this underground network expands, mushrooms can emerge around its growing edge. If the fungus keeps expanding outward, the fruiting bodies eventually form a circle. Simple enough — except that scientists haven’t had an easy way to see exactly what’s happening underneath the grass.
That’s where researchers led by mycologist Hanna Johannesson of Stockholm University came in.
Looking underneath a fairy ring
The researchers focused on Marasmius oreades, commonly known as the fairy ring mushroom or Scotch bonnet. They studied two separate fairy rings growing in a cemetery in Uppsala, Sweden, taking soil samples along lines that crossed each circle.
The samples came from three different areas: the mushroom-free centre, the mushroom-rich edge and the soil outside the ring. The researchers then sequenced DNA from those samples, looking specifically for genetic material belonging to M. oreades.
The results were pretty striking. Large amounts of the mushroom’s DNA were found around the ring, particularly toward its outer edge. In the centre, however, the amount of fungal DNA fell back to levels similar to those found outside the ring. That suggests the ring isn’t simply a neat arrangement of mushrooms sitting above a more conventional underground fungus.
The mycelium itself appears to be forming a ring.
But why?
Is the fungus actually running away?
The researchers considered several possibilities. Perhaps the fungus simply keeps growing outward at a consistent speed. Maybe there is some kind of directional mechanism guiding its expansion. Or perhaps different parts of the fungal network somehow communicate with one another to maintain the circular structure.
There was another possibility, though: maybe the fungus is moving away from something.
To investigate, the researchers dug up sections of the two fairy rings and transplanted or rotated them into different positions.
Then they waited… For 14 months.
When they returned, the results were most consistent with what they call the transient-escape hypothesis.
According to this idea, the soil behind the growing edge of the fungus temporarily becomes less suitable for further growth. The fungus therefore continues expanding into the soil ahead of it, leaving the less favorable conditions behind.
The researchers describe the results as being most consistent with a situation in which the mycelium “avoids inhibitory factors present at the back edge of the mycelial growth front.”
It’s a wonderfully fungal solution to a difficult problem: keep moving toward better conditions.
What is the fungus escaping from?
This is where things get particularly interesting — because the experiment couldn’t establish exactly what is making the old soil less hospitable.
One possibility is nutrient depletion. As the fungus grows through the soil, it could consume resources in its path, making the area temporarily less useful for continued growth. Another possibility is that the fungus releases compounds that temporarily make the soil unsuitable for itself.
Either way, the important word is temporary.
When pieces of the fungus were placed back into the centre of a fairy ring, they were still able to grow. That suggests the conditions aren’t permanently hostile. Something changes over time, allowing the fungus to return later.
The transplantation experiments also produced some intriguing directional results. A section moved completely outside one ring continued growing in its previous direction, while the corresponding experiment involving the second ring produced growth in an additional direction.
Clearly, there’s more going on here than simply “mushrooms like circles.”
Why fairy rings still feel magical
There’s a satisfying scientific explanation for the basic structure of a fairy ring: a fungus grows outward through soil, producing mushrooms along its advancing edge.
But this new research makes the phenomenon even more interesting. Instead of a perfectly programmed fungal circle, the ring could emerge from a much more dynamic process. The fungus grows, changes its environment, encounters less favorable conditions behind itself and continues pushing into new territory.
It’s a little reminder that the hidden mycelial network is constantly interacting with its environment, responding to resources and conditions that we can’t see. Magic!
The science behind the mushroom magic
The researchers are careful to point out that their findings are preliminary. More fairy rings need to be studied, alongside laboratory experiments designed to identify exactly what causes the apparent inhibitory effect.
But the study demonstrates something valuable: researchers can use DNA recovered directly from soil to investigate fungal growth happening naturally underground. That opens up new possibilities for studying fungi in their actual environments rather than relying entirely on what happens in laboratory cultures.
As the researchers put it, this approach could “provide new insight and ignite new questions regarding the processes behind the fairy ring structure and growth pattern."
And there are certainly plenty of questions left. What compounds might be accumulating behind the growing edge? How does the fungus respond to them? How does the mycelium coordinate its expansion? And why do some species form such spectacular rings while others don’t?
For now, the fairy ring keeps some of its secrets.
What we do know is that beneath that apparently simple circle of mushrooms lies a living network constantly negotiating its environment. The mushrooms are only the visible part of the story.
So the next time you spot a perfect ring in a meadow, take a moment to appreciate what you’re actually looking at. There could be an entire underground organism quietly expanding beneath your feet — leaving yesterday’s territory behind and pushing into whatever comes next.
