Garden Myth: Lime to Control Mushrooms

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A fairy circle of mushrooms or toadstools. Photo: Cropcircles, Wikimedia Commons

Do you have mushrooms (fungi) in your lawn, often especially abundant in the fall? Maybe they form a round called a fairy circle. Or a small colony here and there. Their presence can be annoying, but, to be honest, there is no easy way of getting rid of them.

Above all, don’t fall for the old garden myth that you can control mushrooms by liming the soil. That was debunked generations ago, yet is still being repeated, often by garden centers with lime to sell (who should be ashamed to lie so brazenly to their customers!).

Lime has no effect on lawn mushrooms. Photo: http://www.weedmanquebec.com

Behind the lime treatment is a common misconception: that the presence of fungi is linked with acid soil, but in fact, soil pH is not a factor at all. If it were indeed true, lime ought to work miracles. After all, it’s very alkaline. By applying it, you can raise the pH of the soil, making it more alkaline too. And then the mushrooms should disappear, except… 

Fungi are essentially indifferent to soil pH. They grow as readily in alkaline soil as neutral or acidic ones. Thus, by treating with lime, you’ll have wasted time and money … and perhaps also have made your soil unfit for cultivation for many years (the application of lime, if not applied very carefully, can have a pretty devastating effect on plantings).

Now, of course, the advantage to unscrupulous salespeople is that treatment can sometimes seem to work. After all, the mushrooms usually disappear after the treatment … but then, they would have disappeared anyway: most lawn mushrooms are very short-lived and soon disappear even if you do nothing at all. 

The proof of the effectiveness of any lawn mushroom treatment is whether they reappear or not the following year. And after a treatment with lime, they’ll be back: the treatment won’t even have slowed them down!

Mushrooms: Tolerance Is the Key

To be honest, the best thing to do when mushrooms sprout in your lawn is to ignore them. Or chop them down to mow them into temporary submission (a particularly wise choice if you have pets that might eat them). Actually eliminating them is very hard to do.

Here’s why:

What you see is when mushrooms pop up in your lawn are only the above-ground part of the fungus: the sporocarp, its fruiting body. It can be umbrella-shaped, oval, pointed, lumpy, etc. and can come in just about any color imaginable. The sporocarp emerges from underground specifically to release spores so that the mushroom can reproduce (remember that mushrooms grow from spores, not seeds). 

And you needn’t be concerned that these spores will germinate everywhere in your lawn like so many dandelions. The spores are very light and generally carried far away by the wind. Plus, fungus spores only germinate when the conditions are just right: not even one spore in a million actually forms a new colony of mushrooms.

The above-ground part of the mushroom is its sporocarp (fruiting body); the real mushroom is the threadlike mycelium found underground. Ill.: http://www.britmycolsoc.org.uk

The “real” fungus associated with a lawn mushroom, its vegetative body, lurks underground, out of sight, in the form of mycelium: a mass of branching, threadlike, often white hyphae. Only when the mycelium is well established and ready to reproduce does it produce one to many sporocarps. The mycelium can be vast, covering many square yards or meters. All the sporocarps in a fairy circle, for example, stem from a single underground fungus, like dozens of flowers rising from an underground plant.

Not Always Bad

Often, the same mushrooms that so annoy you when they pop up in your lawn are actually beneficial. 

They may be the sporocarps of beneficial mycorrhizal fungi that live in symbiosis with nearby plants, likely trees and shrubs, helping them better absorb minerals and moisture. Others are saprophytic mushrooms, that is, fungi that live on and digest dead wood, probably living off an old tree root or stump. And decomposing dead wood is a good thing!

Also, many of the sporocarps that grow in the gardens are edible … but to verify this, I recommend you contact your local mycological association, because others are poisonous. With literally thousands of species of fungus living in most regions, identification can be tricky.

Fungicides Are No Better

Garden fungicides don’t reach the underground mycelium, so have no effect on lawn mushrooms. Ill.: http://www.marketonweb.fr & http://www.pngguru.com

You’d think you could control mushrooms by applying a fungicide. After all, doesn’t fungicide mean “fungus killer?” But they’re designed to stop the spread of fungal diseases that occur on stems and leaves: mildew, rot, etc. In other words, on fungi with exposed mycelia. Mushrooms and toadstools not the fungus itself, just the sporocarps. The real fungus is underground, where fungicides can’t reach them. 

So trying to control lawn mushrooms with a fungicide is yet another a waste of money.

Dig ’Em Out!

You can try digging mushrooms out. Photo: news.duke-energy.com

If you really want to destroy a mushroom, use its sporocarps, clearly visible, to get an idea where it’s located … and start digging! 

If it’s a saprophytic fungus (which lives on dead wood), look for and remove the piece of wood it’s sprouting from (an old root, a stump, piece of buried wood, etc.): often the wood is near the surface, but it can also be up to a yard (1 m) deep, sometimes even more.

If it’s a fairy circle mushroom, dig up and remove all the soil from within the circle to about 1 foot (30 cm) beyond it. Dig at least 1 foot deep, but if you still see white hyphae in the soil below, dig deeper. Now, replace the soil removed with fresh soil and replant. As some rounds can measure 8 feet (2.5 m) or more in across, it’s a herculean task!

And sometimes all the effort is for nothing: the mushroom simply comes back the following year. You see, if the slightest bit of mycelium is left in the ground, it may just sprout again. Not often, but it does happen. Fungus mycelia are sometimes really hard to eliminate!

Masking the Damage

Grass is greener around a fairy ring. Photo: http://www.greencast.com.au

To camouflage the presence of a fairy circle, give your lawn extra good care. That’s because the turf forming the circle is often greener than the rest of the lawn. That happens because, as mushrooms feed, they release nitrogen and other nutrients to the soil and those stimulate grass growth, resulting a lawn that appears yellow-green compared with the darker green circles. But if you fertilize, top dress, aerate, regularly water and otherwise maintain your lawn, it will be an even green all over and the circle won’t be so obvious.

The Laidback Method

But the easiest thing to do is to either ignore the mushrooms or simply run over them with your lawn mower. See them as a sign of Mother Nature at work … and Mother Nature knows best!

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