When it comes to mushrooms in the soil, there are billions of micro-organisms which are constantly working, eating and decomposing organic matter
in the soil. Fungal fruiting structures release tiny spores that are easily carried in the air to new sites. These spores find a home on organic materials such as a piece of rotting wood and start to grow, sending out thin filaments called hyphae. These hyphae decompose wood, leaves, food waste from compost piles, mulches and organic matter- some develop sufficient mushrooms that grow and appear in your lawn. These fungi can live in your soil for years and when conditions are right, they prosper, such as after periods of prolonged wet weather. Mushrooms are usually found in areas of poor water drainage.
New sod lawn installations and newly reseeded lawns require frequent irrigation and this sometimes promotes the growth of mushrooms. The mushrooms do not harm the lawn and will disappear as the volume of water is reduced.
Removing mushrooms from the top of your lawn will not kill the underground mycelia from which they are growing, so they may return. To manage mushrooms, aeration is necessary to break up the existing dense fungal mat of mycelia. Remove cores at least ¼" to 1 inch in diameter deeper than the fungal mat penetrates the soil. Determine the depth of this mat with a trowel or shovel. You may have to aerate these areas more than once each year to keep ahead of the regrowing mushrooms. This aeration breaks up the fungal mat but also improves water and air penetration into the soil creating a better lawn growing environment. If the fungal mat is more than 3" deep, a shovel or auger may be used to penetrate deeper into the ground. If the mushroom infestation is extreme and you want to completely eradicate mushrooms, you may need to remove the soil to a depth of 12" to 18". Refill the trench with fresh soil and reseed the area. Be careful not to infest any surrounding areas with the contaminated soil! You also may apply fertilizer to help the grass to grow and thrive; this fertilization hastens the breakdown of organic matter.