Congratulations. You have mushrooms growing in the lawn. Many homeowners think that mushrooms are somehow dangerous or indicative of disease, but nothing could be further from the truth. Mushrooms are actually quite helpful to the soil. The only danger by having mushrooms in the lawn is if pets or small children actually eat them, since most mushroom species are poisonous. Mushrooms help nurture a healthy lawn and provide valuable nutrients to the soil.
The most common mushrooms growing in a typical suburban lawn include stinkhorns, puff balls and birds nests. Stinkhorns look like thick fingers sticking up from the lawn, with a black, slightly slimy cap. Although they're ugly and smell bad, they do have redeeming qualities. Stinkhorns attract beneficial insects, and they break down organic matter under the soil into its many components, including nitrogen, which helps green up a lawn. The puff ball mushroom is characterized by round, ping pong ball-sized white caps. When you knock into them, they release a cloud of spores to make more mushrooms. Birds nest mushrooms typically cluster in groups, and do indeed look like tiny nests with "eggs" inside. The eggs are actually the part of the mushroom that contains the spores, the seeds of which will continue to make new mushrooms.
Many homeowners are afraid of mushrooms in the lawn. They think that mushrooms contain disease or will ruin the lawn. The opposite is true. Mushrooms indicate a healthy lawn, with lots of organic matter, such as leaves, branches or twigs in the soil. The more mushrooms, the healthier the lawn. Another common misconception is that picking the mushrooms or running over them with a lawn mower or weed whacker will get rid of them permanently. Every time you disturb a mushroom, you're actually helping it propagate by releasing the spores inside of it. So when you hit it with the lawn mower, you're actually seeding the space with more spores. Whether they grow depends on the conditions.
Mushrooms benefit the lawn in many ways. First, they will decompose organic matter in the soil. This process releases nutrients into the soil to help your lawn grow better. Grass growing in areas once inhabited by mushrooms tends to be lush, green and thick. This is often due to the higher nitrogen content in the soil. If your lawn looks spotty, with patches of dark green from mushroom activity among lighter green, applying more fertilizer to the lighter green areas will often help even out the darker patches and create one swath of emerald green lawn.
The only known risk of mushrooms in the lawn is the risk of poisoning if anyone eats the mushrooms. Although a very small risk, parents know that small children frequently put anything and everything into their mouths. This may include mushrooms. Little ones love to "pick flowers" and may inadvertantly pick mushrooms, believing them to be flowers. Many species of mushroom are poisonous, and it takes an expert to identify safe mushrooms from poisonous ones. If worried about children playing on a lawn infested with mushrooms, simply have an adult pick the mushrooms before children go out to play.
If you're still bothered by the mushrooms growing on the lawn, the only way to totally eradicate mushroom growth is to actually remove the soil where they grow. Probe the soil and look for places where there are mats of growth under mushrooms. Dig up the mat to a depth of 6 or more inches to remove all traces of spores. Remove objects that create environments favorable to mushroom growth, such as stumps, branches and clumps of fallen leaves. But the healthiest way to manage mushrooms is to simply let them run their course. They add more than they take away, and a few days of unsightly, or even smelly, mushroom growth will yield a greener lawn in the future.