I love coming to work on Fridays. I just never know what might be waiting for me on my desk. This morning I had an assortment of oak galls, a very active brown spider (you'll be happy to know it wasn't a brown recluse) and many questions about mushrooms in lawns and, in particular, fairy rings.
Fairy rings typically appear as dark green circles in your lawn ranging in size from a few inches to as much as 15 feet in diameter. In periods of heavy rain or excessive irrigation, mushrooms often grow around the ring. The fungi that cause fairy rings live on the thatch layer and on decaying organic material in the soil beneath the lawn such as: old tree stumps, roots, logs or lumber. Nitrogen released by this fungal activity enriches the grass and causes the dark green color. An area of brown or dead grass may also develop due to the dense growth of fungal strands beneath the sod. Once the decaying material in the soil is depleted, the fairy ring will gradually disappear, but this may take quite some time.
Fungicides are ineffective in controlling fairy rings because the fungal strands beneath the ring make the soil almost impervious to water. Fairy ring damage is rarely serious; your most practical course of action is a cosmetic approach.
When establishing new lawns, make sure to remove tree stumps, large roots and construction lumber prior to planting.
If you have a fairy ring in an established lawn, rake, pick or destroy the mushrooms that appear. Remember that most mushrooms found in Minnesota are extremely toxic, so keep mushrooms away from children and pets, and wash your hands thoroughly after handling them.
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Dethatch and aerate your lawn to encourage moisture penetration of the soil.
Don't overwater your lawn. Remember, excessive moisture and over-irrigation encourages mushroom growth. Reduce the water resistant nature of the fairy ring by using a root-watering wand, or apply a surfactant (wetting agent) to the area to increase permeability and lessen symptoms.
The dark green growth caused by fairy rings is more apparent in nutrient deficient soils. Submit a soil test and apply the recommended levels of fertilizer to the affected area.
In times past, it was thought that fairy rings occurred in spots that fairies had danced. When all else fails, go with that story and enjoy its charm and whimsy. (Of course, I always love a good story and have been known to spread a few of my own.)
For more information about lawn care, visit the Sustainable Urban Landscape website at www.sustland.umn.edu/ and search the topic listing for Sustainable Lawn Maintenance.
Until next time, happy gardening!
"The iron tongue of midnight hath told twelve; lovers to bed; 'tis almost fairy time."
- William Shakespeare,
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A Midsummer Night's Dream
