You wake up in the morning, take the cup of coffee to the patio, sit down, and gaze out into the yard and BANG… mushrooms. It is like the book 'I Spy,' you never know where you will find them. While I have been known to say you can never have too much organic matter, that is exactly the environment that promotes decay fungi, which will provide us that mushroom show. They may be those tiny nearly transparent mushrooms or those large mounds erupting in the lawn.
Mushrooms favor cool air temperatures and ample soil moisture, and we have had that for weeks. The decay of organic matter is natural and should be expected. The decay fungi have been at work all along and the visible part we see above ground is the fruiting structure that if left alone will send out more spores to start a repeat of the natural cycle of decay.
Landscape beds with several years of mulch will often see mushrooms. Take a four-tined digger or hard rake and loosen up the mulch and you will see the fine white mycelial mat supporting the mushrooms above. This also is how you stop the mushrooms from appearing. By loosening the mulch a couple times a season, it dries out and stops providing the environment mushrooms need.
Rotting tree roots in the lawn is another common site. Mushrooms usually do not grow in a line, so if that is what you see, the fungi are following a decaying root in the soil. There continues to be quite a bit of that from all the ash tree roots left behind after the Emerald Ash Borer devastation. No ash you say? Could be a root from the neighbors as the root system can extend two to three times the size of the canopy. With all the winter kill we have had in the home landscape, expect to see more of this over next few growing seasons.
You can have mushrooms in the lawn without buried decaying roots below. The thatch layer is composed of dead turf tissue and other organic matter, such as the leaves you mulched into the lawn last fall. Get the right conditions with adequate decay, and you will see mushrooms. Since lawns can have varying amounts of thatch and thatch layers will dry out quickly, mushrooms from there are temporary. Managing the turf thatch layer by keeping a half-inch of thatch or less, will often times limit or even eliminate the problem. Core aeration and limiting the amount of nitrogen applied will both help keep the thatch layer from building up.
Lastly, Master Gardeners and Horticulture Educators are routinely asked if these mushrooms can be eaten. Among mushroom hunters there is an expression – "You will meet old mushroom hunters, you will meet bold mushroom hunters, you will never meet an old, bold mushroom hunter." The best mushrooms to eat are those you find on the grocery store shelf.