One of the most common types of mushroom seen in a lawn (and the one that most irritates the average gardener) is the fairy circle, a curious phenomenon in which a circle of small mushrooms appears in the turf, usually after a few days of rain.
Often the grass in the circle is greener than the grass on either side. That’s because the mushrooms release nitrogen into soil and that stimulates the growth of lawn grasses. On the other hand, depending on the type of fungus (and there are about 60 species in several genera that can cause fairy rings), the grass may also turn yellow in the center, especially during drier summers, because the soil in the center tends to become hydrophobic (water repellent). If so, puncture the soil with a garden fork and water well to help the grass green up again.
In general, fairy rings will reappear year after year, becoming larger and larger each time, because the underground part of the mushroom, that network of fine white fibers called the mycelium which is actually the true mushroom, grows gradually outward over time. The world record is a fairy circle in Belfort, France, that is almost 2000 feet (than 600 m) in diameter. It is believed to be more than 700 years old.
There are all kinds of legends about fairy rings. They are said to be a meeting place for witches or fairies, a place where they come to dance by a full moon. In general, our ancestors saw them as a cursed place that should be avoided at all costs, especially at night.
The fruiting body of the mushroom or sporocarp (the aboveground part of the mushroom and therefore the part that you see) can be of different shapes and colors. Very often fairy ring mushrooms are edible… but a few are poisonous. Better consult a mycologist before eating any!
Getting Rid of Fairy Rings
Usually the owner of a lawn with a fairy ring only wants to know one thing: what product to apply to kill mushrooms! But in fact there is no product that can kill the mushrooms without killing the lawn. In fact, the fairy circle typically grows out of a piece of buried wood. As long as the wood is still present (it will eventually decompose entirely), mushrooms will keep coming back. That’s why a fairy ring often appears a few years after a tree has been cut down: its dead roots are still present under the ground and are slowly decomposing. And mushrooms are part of the decomposition process. To solve the problem, therefore, you can usually dig around in the soil in the center of the circle and simply remove the piece of wood.
But sometimes the mushroom is more persistent: it has “freed itself” from its original host and is growing independently. In this case, a more radical treatment is necessary: dig up the fairy ring and also circle of lawn about 1 to 2 feet (30 to 60 cm) wide, digging down at least 6 inches (15 cm), and then replace it with fresh soil and reseed with grass seed.
Or you can camouflage the fairy circle by applying a nitrogen-rich fertilizer. That way, the lawn surrounding the circle will be as green as the lawn that makes it up, and therefore circle itself it will be less visible.
As for sporocarps themselves (the part of the mushroom you actually see), if they bother you, just, mow them down with a rake, a lawn mower or even your shoe. Problem solved!
How Not to Get Rid of Fairy Rings
Despite the popular belief that mushrooms grow only on acid soil, the presence of fairy rings and other fungi in the grass is no way connected to the soil’s pH. The mushrooms are non-sectarian: they’ll grow just as readily on alkaline soils as acid soils. So applying lime will not work: a waste of time and money!
What Should a Laidback Gardener Do?
Personally, I suggest doing nothing when you see a fairy ring in your lawn. It’s a totally natural phenomenon, highly intriguing, and it makes a great story to tell your children and your grandchildren. And is it really so bad if something natural occurs in the artificial environment we call a lawn?