Heavy rains or prolonged rainy periods often encourage the growth of mushrooms (toadstools) in lawns and other turf areas. Most often, the mushrooms will appear randomly across the lawn. If the mushrooms emerge in more organized circular or part-circle patterns, they are the fruiting bodies arising from a soil-inhabiting fungus. This condition is popularly referred to as “fairy ring”. Fairy rings may be from 1 to 12 or more feet in diameter; mushrooms may never be seen with some fairy rings, or may emerge only during rainy weather. Once they appear, fairy rings often continue to grow and enlarge for many years.
All lawn grasses are susceptible to fairy rings and several species of mushroom-producing fungi may cause them. Aside from the occasional appearance of mushrooms, the most common effect of fairy ring fungus is the formation of darker green, stimulated rings of grass. The stimulation of growth and color is caused by the release of plant nutrients to the turf as the fungus decomposes organic matter in the soil. Less commonly, the soil just inside the ring may become so filled with the fungus that water penetration is prevented and the grass dies. When the only effect of a fairy ring fungus is a ring of taller, greener grass, a modest increase in nitrogen fertilization over the entire lawn can help mask symptoms. If fairy ring has caused significant grass death, then renovation (heavy core aeration, followed by over-seeding with the appropriate species) may be necessary.
Fungicides are not recommended for the control of fairy ring and mushrooms in the lawn. Because mushrooms are merely the fruiting bodies of fungi living in the soil, removing them does not kill the underground part of the fungus. While picking mushrooms soon after they appear may prevent spores from spreading in the lawn, the primary reasons for removing them are to protect children and pets and to improve the lawn’s appearance.
Mushrooms found growing in lawns should NEVER be eaten, unless you are well acquainted with the different species. Many mushrooms are poisonous to some degree and ONLY an expert can distinguish between edible and poisonous species. Since young children and pets may be tempted to eat mushrooms, remove the obvious fungal structures by raking, mowing, or hand-picking can avoid the possibility of poisoning or illness.
For more information, see the following Planttalk Colorado™ video(s).