Fairy Rings are natural and can be explained unlike crop circles. Fairy Rings are the natural formation of Mushrooms and / or Toadstools which form and grow on your lawn, but mainly in woodlands.
The mushrooms do not start in a circle but in a clump, season after season the spread out into a circle which gets larger and larger season after season.
At some point in history, some wood has been buried under your lawn or a tree had fallen / cut down leaving its roots under your lawn. After time the dead wood will start to decompose, and this releases Nitrogen. The Nitrogen release explodes outwards in slow motion, working its way through your soil. The circle of Nitrogen gets larger and larger, year on year.
The large build up of Nitrogen is visible in your lawn, commonly seen as dark green circles of lush grass in the lawn usually after they are a half a metre or so across, though they are visible at first as a tuft of dark green grass.
The Fairy rings may also be first noticed as a group of toadstools manifest in mid-summer. (Sometimes without the dark green grass!) Not all toadstools in the lawn are as a result of Fairy Rings.
Fairy rings start growing from a central point, then gradually radiate outwards in circular shapes. There may be several fairy rings in the lawn at the same time sometimes overlapping - ending up not unlike the interconnected Olympic flag symbol!
Generally, the grass inside the circle is lighter green - if not brown, whilst the grass just outside the circumference of the circle is slightly darker. This a result of Nitrogen being released - or activated.
No, not always, but if they do form one year, they will come back year on year.
The rotting and decomposure of the wood can cause a reaction called Mycelium, Mycelium is the birth of Mushrooms and Toadstools which feed off the Nitrogen, therefore as the Nitrogen spreads, the Mushrooms and Toadstools follow.
The lush dark green grass is a result of nitrogen being released by the fungal activity as the ring spreads outwards. As the fungi (toadstools) spread outwards they feed on decayed matter (dead grass roots and other decaying matter) and release Nitrogen into the soil behind them. The live grass in the area feeds upon this Nitrogen, which in turns it a dark green. Thereafter the fungi take hold proper and leaves behind it, a weakened central are of the Fairy ring in your lawn. This is how the Fairy Ring becomes visible.
Sometimes the fairy rings are made up of two circles - an outer and inner circle, with dead grass between. This is normally bought about in highly compacted soils, when the rainwater cannot penetrate down to the grass roots. At the first sign of fairy rings, aerate the area with a fork, to about 15cm (6in) deep, and drench the area with water, thereby allowing the moisture to penetrate into the affected area of soil. This is not a 'remedy' as such, but does have an affect upon the strength or weakness of the rings.
Fairy rings in lawns normally start to show up in late spring or mid-summer. They then carry on growing right through until the autumn and usually into subsequent years. They are easily recognised by either of two or both trademarks. Once they have started, they will be visible throughout the year.
Fairy rings are rarely fatal to lawns, which is satisfying to know, as there are no chemical remedies for use in UK gardens.
The best method is tedious but effective and Not a 100% but it is the best method. Firstly, you have to release the Nitrogen trapped underneath your lawn. You can do this by inserting a fork 3 to 4 inches (10 to 12 cm) down, give it a little wriggle and repeat it all the way around the circle. This will oxigenate the land and release the Nitrogen build up. Repeat this for a couple of days and then flood the area until you have standing water. The next day repeat your forking process, this will break down your lawns substructure and release the Nitrogen and without the food source the mushrooms should not return.
You can lightly feed the lawn with a general lawn fertilizer. Do NOT over-feed, for this will eventually weaken the grass. But, a weak feed will darken the rest of the lawn to the same colour as the fairy rings!
The other option is to dig out the soil where the fairy ring is growing to a depth of up to 90cms, and refill with sterilized loam! This method is also not fullproof, as you can never be certain that you have removed all the fungi and Nitrogen.
There is alot of Folklore regarding Fairy Rings dating back to Celtish times. It is said the Ring of Mushrooms are formed to give fairies a rest. Fairies would dance around in a circle around the fairy village, which is believed to be hidden under the circle. When the fairies were tired they would sit on top of the Mushrooms.
There is a belief that if you step into the fairy ring, it will bring you good luck. Another belief is that it will bring you bad luck because you are stepping on to the fairy village.
Another belief is that if you join in the fairy dance within the circle under the moon you can be sometimes lost to time and place and may even disappear forever.
This is English Folklore, passed down through the centuries, who are we to question it.