The sudden appearance of mushrooms on the lawn can sometimes seem magical, especially when they are arranged in a circle. These so-called fairy rings may be a foot in diameter or 100 feet across. They typically enclose darker green grass.
BIOLOGY: More than 40 species of fungi are responsible for the so-called fairy rings found on lawns. These fungi are saprophytic, feeding on dead organic matter of various types, from buried stumps to thatch. Their feeding releases nitrogen, which in turn enhances the growth of vegetation in their vicinity, producing irregular arcs or circles of darker green turf. These circles range from a few inches to more than 50 feet in diameter.
SYMPTOMS: A band of fungal spore-producing fruiting bodies (mushrooms or puffballs, depending on the species) may appear annually at the outer edges of these patches in moist weather. Such bodies and the associated areas of darker green grass are the most common symptoms. Occasionally, fairy rings enclose patches of dead turf-the result, it is believed, of ammonia or some other toxic by-product buildup, or simply from the drying-out of soil associated with the growth of the fungal mycelia.
CONTROL: Fairy rings are very difficult to control. There are no fungicides available for homeowner use, and removing the soil to a depth of 12 inches and replacing it with clean soil and new grass seems excessive. Fairy rings can be avoided by not burying stumps and other organic matter beneath future lawns. Raking away mushrooms that have appeared and applying nitrogen fertilizer to the surrounding turf will erase much of the evidence of fairy rings. But the simplest response is to enjoy these mycological manifestations, whether they prove the existence of fairies or not.