Ways to stop mushrooms from growing in a yard include: reducing irrigation, aerating the soil, dethatching dead grass, removing pet waste, disposing of rotting mulch and removing old tree stumps. The mushroom is merely the flowering part of a fungus and picking the mushroom that sprouts from the ground is not enough to kill the mycelia beneath the soil. Mycelia are the foundation "threads" which connect mushroom spores underground and allow them to grow into full-fledged mushrooms.
Some mushrooms form due to buried construction materials, dead tree roots or other buried organic matter. Old mulch, pet waste and decomposing tree stumps are a great source of food for mycelia. In order to remove mushrooms permanently, food sources must be removed from the environment.
Mushrooms typically do not usually harm the grass and are actually beneficial to the garden as they release more nutrients into the soil. Using a nitrogen fertilizer may help speed up the decomposition of the organic matter and get rid of the fungi's food source faster.
While picking mushrooms will not kill the mycelia, removing them as soon as possible may help stop the spores from spreading to a new part of the yard. If newly laid grass requires frequent irrigation to help establish it, mushrooms may grow. They will usually vanish once the extra irrigation is stopped. Fungicides are generally ineffective against the mycelia underneath the ground as it does not penetrate far enough.