Mushrooms, sometimes called toadstools, are the reproductive structures of certain types of fungi. They contain thousands of spores carried by the wind. Most fungi that live in lawns are beneficial because they decompose organic matter, thereby releasing nutrients that are available to the plant. Because of this, areas of lawn where mushrooms are growing may be darker green in color.
Mushroom fungi don’t attack lawns directly. The fungus grows underground and consists of a network of filaments, tiny threads that resemble cotton. But at some point this mass of fungal cotton will die and due to its hydrophobic or water repelling characteristic, will form a dense mat that repels water. This will cause the soil beneath it to be dry. Even though the lawn receives ample water, brown areas will appear due to the repelling effects of the mushroom mat.
The underground fungal structures can grow in the soil for years. But when conditions are right, after periods of prolonged wet weather, mushrooms will appear. Picking mushrooms soon after they appear may prevent their spores from further infecting the lawn, but new spores will blow in, and the underground fungal growth still remains. The primary reasons for removing mushrooms from lawns are to keep them away from children and pets and to improve the lawn's appearance.
If significant dying or dead areas occur in the grass, lawn renovation may be required. If the grass is not dead, it can reestablish itself if water penetration is improved by breaking up the dense fungal mat. This can be done by removing cores of soil that are at least 1/4 to 1 inch in diameter and slightly deeper than the fungal mat. The use of a lawn aerator a few times a year may be sufficient to improve water penetration.
Predisposing factors for mushrooms developing in a lawn are
- Buried wood in the landscape (tree logs, limbs, dead roots, construction lumber)
- Stressed or under-nourished turf
- Excessive irrigation
- Heavy or unmanaged thatch
- Poor soil aeration
Do not eat these mushrooms or other fungal fruiting bodies unless you are well acquainted with the different species. Many species are poisonous, and only an expert can distinguish between edible and poisonous. There are no simple tests that can be used to identify poisonous mushrooms.
