Info from Almanac dot com
A fairy ring marks the edge of an underground mycelial network. Magical-looking, but perfectly natural! From a scientific perspective, fairy rings occur when mushrooms grow in a circle, arch, or other pattern that looks almost deliberately planted. These circles often seem to pop up overnight, but they actually emerge only when conditions are just right for mushrooms. That usually means lots of rain and cool weather!
Like fruit on an apple tree, the mushrooms that sprout above ground are the “fruiting bodies” of a much larger mycelial network in the soil that feeds on organic matter. However, as the organic matter is depleted by hungry mushrooms, the mycelial network spreads outward in search of more nutrients. This creates the circle-like formation, which we know as fairy rings. It’s a natural process—but one that feels almost enchanted when it appears overnight on your lawn.
According to the lore of the British Isles and Scandinavia regions, fairy rings were created by elves or fairies dancing beneath the full moon. When the merry dancers grew weary, they used the toad- stools as seats to rest on or as tables for feasting.