Mushrooms produce tiny seed-like bodies called spores, which easily blow about in the wind. When these spores reach a favorable place to grow they germinate and send out long thread-like growths called hyphae. A single strand of hyphae is too small to see without a magnifying glass. Sometimes the hyphae grow together in the soil to form masses called mycelium. When the mycelium has developed sufficiently, mushrooms are produced. The mushroom-producing fungi can live in the soil for years and produce mushrooms whenever the weather is favorable.
It’s important to understand that the mushrooms, which are now visible in lawns, are developing on thatch (decomposing grass leaves and stems) or dead tree roots. The fungi that produce the mushrooms are harmless to grasses and landscape plants. Although mushrooms, toadstools, puffballs and other assorted fungi may be unsightly, they also indicate something good is happening in the soil. These growths are only the top portion of an extensive fungus organization in healthy soil that is breaking down organic material.
In the process of decaying particles and changing them to humus, various mineral elements and nutrients are released from the organic material by the fungus growth. Mushrooms and toadstools are not usually damaging to the grass, but they may disrupt the appearance of the home landscape. To remove them, simply mow the lawn or rake them out of the grass. They will disappear when lawn conditions become drier or the outdoor temperatures become colder.
There are no chemicals (fungicides) that are effective in controlling mushroom producing fungi. If the mushrooms are coming from dead roots, the best control is to dig the roots up. If excessive thatch is causing the problem, then de-thatching the lawn in the fall is the best solution. De-thatching removes the fungi’s food source. Simply removing mushrooms may make you lawn look better, but it will not kill the mycelium from which the mushrooms grow.
In lawns, mushrooms sometimes grow in circular patterns called "fairy rings". Fairy rings are caused by certain fungi, which may or may not produce mushrooms. In some cases, the soil in the ring becomes so matted by the fungus mycelium that water cannot move through it. As a result, the grass in the ring grows back poorly, and may actually die from the lack of water. The best solution to this problem is to aerate the soil in the ring, then water deeply. This should improve turfgrass root growth and eliminate, or at least reduce the effects of the fungus.