Mushrooms are the fruiting structures produced by various fungi. The appearance of the
mushrooms varies depending on the fungi species. The fungi are present beneath the
soil surface all along, but when conditions are right, they are able to set fruit. The result
is mushrooms popping up in the landscape.
Warm, moist conditions tend to favor mushroom development. Beneath the soil the
fungus feeds on decaying organic matter. Rainy weather speeds up the decay which
gives a boost of nutrients to the fungus allowing it to have proper nutrition for fruiting.
Therefore, the appearance of mushrooms is often an indicator that the soil is healthy
and has a good level of organic matter.
Though many of the mushrooms are harmless to our plants, some can cause or indicate problems. Fungi mycelium grow underground from a center point outward in a circular pattern. When the conditions are favorable, mushrooms appear on the outer edge
of the ring above the soil surface in an arc or circular shape. In lawns this is called a fairy ring. This can cause problems in the lawn as the mycelium can form a dense mat that decomposes organic matter and releases nitrates into the soil. The lawn in the outer area of the circle grows more rapidly and turns a darker green color than other areas of the lawn. The mycelium mat can also reduce water infiltration and there may be some turf dieback in this area.
Fairy rings are difficult to control. You can sometimes eliminate the ring by digging to a
depth of 6 to 12 inches by 12 inches wide inside and outside of the ring, refilling the hole
with non-infested soil. Those in commercial businesses will sometimes use a fungicide
to control fairy rings but these products are not available to homeowners. See
http://www.ksre.ksu.edu/bookstore/pubs/EP155.pdf for more information on these
fungicides.
Mushrooms will disappear as the weather dries out again or when it gets colder. The
fungi remain beneath the surface ready to send up fruit once conditions are favorable
again. Because most mushrooms are harmless to the landscape there is little need to
try to control or prevent them.
