Fairy Ring Mushrooms
Underground fungal colonies can radiate outward in all directions and
sometimes form a circular pattern.  Fairy rings or fairy circles, are
common names for this phenomenon, and are most apparent in mowed
fields and lawns.  Field rings is another term, although woodland
mushrooms will also exhibit circular patterns of growth.
Fungi in the soil interact with grasses, consuming organic material in dead
grass and by exchanging nutrients with live grass.  The above fairy rings are
the work of the meadow mushroom.  Note lush grass (first growth of spring
before being mowed) where the mushrooms appeared the previous autumn.  
October 2008
October 2008
April 2009
April 2009
Google Campus, Mountain View, CA
See also Fairy Rings at
Mycorrhizae And Turfgrass
Many different mushrooms form fairy rings. These examples are of
Agaricus campestris, the edible meadow mushroom. School yard.
Park behind city hall, Hammond, IN
Field near urban development,
Indianapolis, IN
Farm house, Smithville, IN
Google Earth images showing fairy rings:
mushroom fairy ring
mushroom fairy ring