Mushrooms grow in lawns because of organic matter or wood growing under the sod. The fungi helps decompose organic matter in the soil and does not harm the grass, but your lawn may look unsightly at times. The mushrooms, which may attract children and pets, may be poisonous so it is important for you remove them. While you can rid your lawn of the fungi through careful, persistent control, the wind may introduce new spores into your yard.
Most mushrooms form from dead tree roots, buried construction lumber or other organic matter under your lawn. The fungi grow underground with the fruiting body you see above ground produced to help the spores spread. The mushrooms only appear above ground when conditions such as wet weather prevail. Otherwise, the mushrooms may not appear for years.
Fairy rings form circular rings from 1 to 12 feet in diameter in your grass. Several species of fungi may produce the rings, but not all fairy rings produce fruiting bodies. Instead, you may see rings of stimulated grass growth forming arcs or circles. The growth comes from decomposition of organic matter by the fungi. Sometimes fairy ring causes dead areas of grass, requiring control to get the lawn healthy again.
The fruiting part of the mushroom releases tiny spores into the air. Once the spores find a good spot to grow, they germinate, sending out hyphae. Hyphae consist of long, think filaments that help break down wood, leaves and other organic matter as food. While individual hyphae remain invisible without a magnifying lens, clumps of hyphae sometimes resemble masses of white or dark threads. These threads, called mycelium, eventually produce the fruiting bodies seen above ground growing in the lawn.
Since no chemical control exists to control mushroom growth in your lawn, you must remove the fruiting heads with a garden rake or lawn mower. To permanently remove the fungi, you’ll need to dig up and remove the wood on which the mushrooms grow. Picking mushrooms as soon as they appear may keep the spores from spreading to other areas of the lawn. For fairy rings, you need to break up the dense fungal mat that grows below the grass. Breaking up the mat may involve the use of a shovel, aerators, soil probes or small augers. For mushrooms that appear in new sod, decreasing irrigation helps control growth of the fungi.