With a cute name like "fairy ring," you would expect to see a bunch of storybook characters cavorting around on your lawn, but that is not the case at all. Fairy ring is the name of turf damage done by Basidiomycete fungi. 

Identifying Fairy Ring

There are three types of fairy ring fungi; one that produces only a ring of hyper-green grass, one that produces a green ring and mushrooms, and one that just produces mushrooms. These rings can be as small as one foot in diameter and as large as 10 feet across, and may be a complete or just a partial ring. All  species of turf grass in both cool and warm climates are susceptible to fairy ring fungi. Since they feed on decaying organic matter, they sometimes spring up around a spot where a tree stump has been ground, or where there is some other type of decaying wood

Conditions Favorable to Fairy Ring

As with all lawn fungus infections, fairy ring needs moisture to survive. They commonly occur in lawns with too-frequent irrigation or bad drainage, but can survive under many different soil conditions. They often infect lawns that have a thick thatch layer which they can convert into nitrogen, forming the dark green ring color.

Dangers of Fairy Ring Mushrooms

While the fungi are not usually fatal to turf grass in and of themselves, as they move through soil, they compact it, which prevents water from penetrating to the roots. This is what causes the browning and thinning of grass often found right outside the ring. Fairy ring mushrooms are toxic to pets and humans, so it's best to remove them as soon as possible if you have pets or children that play on the lawn.    

Controlling Fairy Ring

After fairy ring has taken hold, there is no way to kill it, with no current product on the market being effective. The best way to control these fungi is to prevent them. Remove thatch and other organic matter from your lawn that they can feed on, such as old stumps, sticks, and leaves. Water deeply and less frequently to deny them the moisture they need to survive. Aerate the soil to prevent turf death by compaction. Fairy ring fungi usually persist for only four to five years, then outgrow themselves. In the meantime, you can disguise the problem by using nitrogen fertilizer on the rest of your lawn so the rings are not as obvious.

Fairy ring fungi are a common problem in lawns that are over-irrigated and have bad drainage. They can strike in almost any climate and survive in almost any soil conditions. Talk to your local lawn care specialist (such as one from Green Leaf Lawn Services) about how to best control fairy ring in your lawn.