Answer: Fairy ring fungus is common in lawns in your area because of the high rainfall. It is actually a mushroom mycelia growing under the lawn that is causing the rings. While there are many temporary methods to getting rid of lawn mushrooms, the only permanent solution is to remove their food source. Food sources for soil fungi can include:
Decaying tree stumps
Decaying tree roots
Once all the food sources are exhausted, and the lawn soil infested with the mold spores is removed, your lawn mushroom problem will be permanently solved. There are many temporary solutions, including:
Continual removal of actual mushrooms
Chemical removal of actual mushrooms
The above methods can be temporarily effective, but they can be time-consuming, and do not help in permanently getting rid of lawn mushrooms. The only way to permanently get rid of lawn mushrooms is to exhaust their food source, and remove all soil that may contain traces of the fungi. The mycelia can spread 2' deep. This sounds drastic, but the mycelia can really spread, so digging out all the affected soil to a depth of 2' is what is recommended by Oregon State University.
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