Master Gardener: Will your lawn mushroom?
By Helenruth Schuette
There is only one mushroom I look forward to seeing in my lawn and that’s the morel mushroom. We have had four in one year, and five in another, depending on the spring moisture and warm-up. To promote this harvest, we leave the area alone until after Memorial Day when morels are usually seen. As I write this, it has been too cool for mushrooms to spring forth even though it has been wet enough. According to Bob Mugaas, University of Minnesota extension educator, after moderate to heavy amounts of rainfall, mushrooms begin to randomly appear in lawns. Their appearance often causes people to be concerned about the health of their lawn and whether or not a serious disease might be getting started.
It’s important to remember that mushrooms are the ‘fruiting bodies’ of fungi living in the soil and thatch. The vast majority of those fungi are not associated with any lawn disease-causing organisms. It’s quite common for them to appear during periods of moist conditions resulting from either natural rainfall or excessive irrigation. Again, they are not necessarily indicative of any particular lawn problem.
The fungi are living on decaying organic matter in the soil and/or thatch layers. This breakdown of organic matter results in at least some of the nutrients contained in that organic matter being released back to the soil. At this point, the nutrients are available for continued plant growth or used by other microorganisms. If you find mushrooms offensive, simply knock them over with a rake and remove them from the area. Most mushrooms disappear when dry weather returns.
Mushrooms in lawns are also commonly associated with poor drainage. Removing excess thatch and aerating the soil to improve water penetration in the lawn can help in some cases. Lawn mushrooms often begin over the top of trash wood buried in the soil or tree roots left behind when a stump is left behind. If that’s the case, the mushrooms will stop showing up when they’ve done their job, which is to turn that wood into soil.
There is one exception to the above situation known as fairy ring. They are the most common lawn mushroom. Symptoms in the lawn appear as dark green arcs and/or circles; often darker than the surrounding grass on either side of the ring or arc. These mushrooms actually increase the nutrients available to the grass, creating areas of lush, dark green growth often in the form of a circle. To prevent fairy rings, properly water, fertilize and de-thatch lawns. Fairy rings are most common on sandy soils that are low in water and fertility. Thick thatch layers also contribute to this problem. Eradication of fairy ring fungi is difficult and often impractical. If mushrooms are the only evidence of fairly rings, remove them by picking or raking and destroy.
The Irish consider fairy ring good luck. As the legend goes, fairies sit on the mushrooms and have parties, bringing good luck to the household. You may have the perfect lawn and still see an occasional mushroom; be thankful for the moisture. And remember this invader, unlike a weed, is easy to knock over and rake away.
For more information about lawns and other horticultural topics, go to the University of Minnesota Extension website www. extension.umn. edu/gardeninfo/. Master gardeners will answer your gardening questions via a voice-mail service. Call 444-7916, leaving your phone number, name and the nature of your question. A volunteer master gardener will give you a call to speak with you.