Q What exactly are fairy rings?

A The term fairy ring is used to describe the visible effects of particular fungi growing in lawns. All affect grass growth and some also produce toadstools.

The rings are formed as the feeding threads (mycelium) of the fungus spread outwards from the point of infection in ever-widening circles.

Caption: Fairy rings appear in summer and autumn

Q What damage do fairy rings cause in turf?

A Affected areas of grass die, due to direct competition with the fungus for moisture and nutrients. The dense fungal mycelia, which grow to a depth of 20-45cm, prevent water penetrating the soil. The fairy-ring fungus also stimulates grass growth at the periphery of the infection, resulting in rings or bands of lush grass.

Q When are the symptoms of fairy rings likely to be seen?

A Fairy rings are composed of three zones. During the summer, the outer and inner rings are marked by lush, dark-green grass and the middle zone of grass will be brown or dead.

The slender, brown-capped toadstools of the fungus Marasmius oreades, the most disfiguring of the fairy-ring fungi, appear in summer and autumn, particularly during periods of wet weather. The ring of toadstools marks the outer part of the area infected.

Q If toadstools appear in circles without lush grass, is the fairy-ring fungus to blame?

A There are other species of fungi, such as mycena and coprinus, that can grow in lawns. Some of these may grow in rings, but without the peripheral lush, green grass characteristic of Marasmius oreades. The toadstools of mycena are short-lived and disappear quickly.

These are likely to be feeding on woody, decaying organic matter, such as tree stumps, the rotting roots of trees that have been felled, or the remains of old shrubs. In order to prevent toadstools of these fungi, it is advisable to dig the woody material up and replace the turf during the autumn or winter.

Q What should I do if my turf is infected with fairy-ring fungi?

A Any toadstools that appear should be raked off and disposed of before they have a chance to spread their spores. If infections are recurrent, the lawn mower should be washed down with disinfectant after mowing the infected area and the cuttings disposed of.

If fairy rings are spotted before the grass in the middle ring of the infected area dies, the water-repellent effect of the fungal threads can be eased. Irrigate the affected area with water containing a few drops of a mild liquid detergent, which acts as a wetting agent helping the water penetrate the soil. Adding a lawn fertiliser to the whole lawn will green it up, hiding the rings.

Q Can I prevent a fairy ring from spreading?

A Fairy rings occurring close to the edge of a lawn will gradually die out, as the fungal threads have no new turf to infect.

If an affected spot is really precious, the turf can be cut out and replaced. But you’ll also have to remove soil to a depth of 50cm, and to extend removal of turf and soil to at least 30cm beyond the outer ring of infection. Infected soil and turf should be disposed of before replacing with a fresh supply. The vegetable plot will not come to any harm if the surplus is mixed with soil there.

Q Are there any chemicals for the control of fairy rings?

A There are no chemicals available to gardeners for the control of fairy rings. However, there are chemicals available to landscape contractors which require trained, licensed operators to be used safely and legally. These professionals will have the correct safety equipment too, so it might be worth calling them in if fairy rings are a persistent problem. Which? Trusted Traders can help you find someone in your area.