What Causes Big Dark Green Circles in Your Lawn?

Big dark green circles in lawns are often referred to as "fairy rings." The term originated from the superstition that the mushrooms which commonly grow within the circles were the paths on which fairies once danced. They are a common nuisance wherever there is a source of decomposition occurring in the soil. They can grow on any lawn or patch of grass---front yards, golf courses, parks or pastures----and are very difficult to control.

The large green circles sometimes produce mushrooms within their centers, often forming arcs. Other circles might have rings of dead grass in the center. However, depending on the season, these patterns might change. The rings have been known to expand throughout the year, growing up to two feet wide and up to over 100 feet in diameter. They can also have long shelf lives. Some have been known to age at least a hundred years.

One of the main factors for the cause of big dark green circles in lawns is the growth of fungi within the soil. Fungi, dependent on decomposing matter, grow prominently in areas where the roots of a tree that has been cut down are decaying or where a thatch of grass on the lawn has grown too thick.

The dark green circles are actually formed when the fungi break down organic matter in the soil and produce nitrogen at very high levels. Mushrooms are visible signs that organic material is being broken down. The fungi actually grows underground in a centralized mass that spreads out in all directions in fibrous growths. This mass is called a mycelium. As the mycelium spreads in different directions in the soil, it forms a circular pattern. As the fungi breaks down the organic materials in the ground, the lawn mirrors this circular pattern. The circle's dark green colors are caused by the nitrogen-heavy gases formed by the decomposing materials.

Absolutely nothing can be done to get rid of the big dark green circles in lawns. While there are some chemicals on the market that purport to solve the problem, they are inconsistent at best in removing the fairy rings. A few things can be done to disguise the patterns. Fertilizing areas surrounding the circles is one such solution. This will introduce equal amounts of nitrogen to the grass, balancing the different shades in the lawn. The dark circles operate on low fertility conditions, so only low rates of nitrogen is necessary to balance the contrast of shades. The mushrooms can be removed temporarily by raking or mowing them.

Prevention is the best chance of decreasing the possibility of fairy rings from appearing in lawns. This can be done through continuously maintaining and caring for the lawn and removing any remaining tree stump materials from the ground.