What are fairy rings?
Fairy rings, also known as fairy circles or pixie rings in lawns and pastures may be caused by one of many species of fungi present in the soil but the mushroom fungus (specifically Maramius oreades) is usually the culprit. Fairy rings may or may not have mushrooms growing around their perimeter but the mushrooms are not the cause, they form as a result of the body of fungus (or mycelium) growing under the surface and usually appear after heavy rain. The mycelium grows outward by as much as 20 – 30 cm (8 – 12 inches) per year and the decaying organic matter that the fungus feeds on, stimulates the soil ahead of it with a burst of nitrogen, which is why the circle is darker green.
The mycelium grows in a web like fashion just below the surface preventing water from penetrating the soil and when a food source like thatch, an old root system, tree stump or any decaying organic matter in the soil is depleted, the fungus stops growing.
One method of controlling fairy ring is to poke holes or aerate the sod and follow with a deep watering. The object is to break through the web allowing water to get down to the grass roots and stimulate new growth. Aerate to about 25 cm (10 inches) deep and 10 – 15 cm (4 – 6 inches) apart. Adding a wetting agent to your water will help maximize the penetrating properties of the water. A wetting agent is basically a surfactant that reduces surface tension or keeps water from beading and allows it to soak into the affected soil. Wetting agent mixtures are available at garden centres — a squeeze of dish soap in a two gallon watering can will also work.
Excavate fairy rings
Another way to minimize damage caused by fairy rings is to dig them up but unless the food source for the fungi is completely removed the fairy ring will probably return within a few years. If the ring is a manageable size, dig to a depth of about a foot below the mycelium layer and extend about 2 feet outward, then dispose of all affected lawn material, refill with new soil and reseed. Unless the ring is small, digging it out would be difficult especially knowing the fairy ring may come back.
Fairy rings won’t cross paths
Fairy rings are nearly impossible to get rid of but here’s a ray of hope — when two fairy rings come into contact, the fungi in each ring appear to inhibit growth of the newly encountered fungi and both rings die. Knowing this, you might dig up some sod including a bit of the mycelium layer from each ring and mix it into the other. Then reseed the cultivated areas of both rings and let nature take its course.
My recommendation for controlling fairy rings is to aerate deeply and soak the ground. Maintain a fertilizing schedule starting on the May long weekend, again early in July and then again on the September long weekend. Mow the lawn to a height of about three inches and avoid frequent shallow watering. Water the lawn to a depth of at least 6 inches less frequently to encourage the roots to grow downward into the soil.
Fairy rings are one of the oldest lawn problems on record and there’s endless documentation about attempts to control them; if you have suggestions about methods that have worked for you, please add your comments, and thanks!
Reference:University of Saskatchewan, college of agriculture and bioresources
Photos: wikimedia commons