Large White Mushrooms Growing In the lawn Are A Community of Fungi Recycling Organic Matter

After heavy rains, high humidly and warm nights, it is not uncommon to have large white mushrooms growing out of your lawn in the morning. Often these mushrooms form a circle or an arc on the outer edge of a circle of darker greener turf. This is a fairy ring.

Fairy Ring History

Fairy Rings are a community of fungi and start from a single point – a piece of nutrient rich organic matter like an old tree stump. The community of fungi thrive on organic matter in the soil and radiates outward from that starting point to form an expanding circle. One fairy ring in France is nearly ½ mile in diameter. The occurrence of these rings is associated with folklore and superstition in nearly every culture where the rings occur. It is the Celtic folklore of the ring that tells tales of fairies dancing – in a circle of course – where we derive the name “Fairy Rings”.

Fairy Ring Facts

Back to reality, the rings are part of God’s creation and master plan. The fungi are saprophytic, deriving food from dead organic matter and recycling dead roots, plant leaves, etc. into usable nutrients for the fungi and higher plant forms. Most of the calls I receive about Fairy Rings are from customers complaining of mushrooms, large white mushrooms, green circles or sometimes dead circles in their lawn. In Pinellas County the fairy rings are a nuisance and rarely damage a lawn.

The Fairy ring has some distinctive characteristics:

1. They form perfect circles or sometimes lobed circles
2. The ring is defined by dark green grass
3. The presence of large white mushrooms growing in a circle or arc
4. Sometimes the inner part of the Fairy Ring has weak, stressed or dead grass

Fairy Ring Biology

The reason for these distinctive characteristic is simple biology – nothing to do with fairies.

• The outer most ring is the mushroom ring, where the fungi is most active and produces the “fruiting structures” or mushrooms.
• The next ring inward is the dark grass ring caused by the release of nitrogen and other nutrients from the activity of the fungi.
• The next ring inward is the area where the fungi have died and left behind a mycelia mat. This mycelia mat is a dense network of thread sized filaments that forms a barrier to water. This barrier is hard to wet and easily dries out, stressing the turf to the point of thinning and sometimes death.
• The next area inward is the normal ring, where after the flush growth, nitrogen release and mycelia mat has very little influence on the soil and the turf.

Fairy rings are a nuisance in lawns that receive good water, medium amounts of nutrients and regularly mowed. The most distinctive nuisance is the green ring and presence of mushrooms. Only in weak, un-irrigated lawns would Fairy Rings “kill” turf. There is no cure for Fairy Rings – at least not economically. The fungi are soil borne and exist everywhere. The food source is organic matter which is part of the turf eco system.

Best Management of Fairy Rings

The best management practice for Fairy Ring in St Augustine grass is:

• Keep the soil moisture and nutrient levels medium to medium high
• Frequent mowing maintaining a canopy height of 4” or above.

These two simple management practices will lessen or rid the visual impact of the fairy ring – the green ring and mushrooms. The physical problems are little more difficult to deal with and you may still see weak thin grass in the interior of the Fairy Ring. If the Fairy Ring causes damage, aerating with a pitch fork or spading fork will break up the mycelia mat and allow for the St Augustine to recover. Regardless, the St Augustine should survive or completely recover especially if the soil moisture and fertility levels are kept at medium to medium high. In every instance the Fairy Ring will grow beyond your lawn and out of sight. FYI: Do not eat the mushrooms. Most of the ones associated with Fairy Rings are considered dangerous and can cause severe intestinal discomfort.