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Ask Sam: Why Are There Crop Circles On My Lawn?

David Leins

Every other Friday on Morning Edition, Outside/In host Sam Evans-Brown tackles a question from a listener. 

David Leins from Dearborn, Michigan, asks: “It’s spring time, and we can see the grass now and it’s even growing a little bit. And I’m wondering why I’m seeing these circles of growth — of greener grass than the rest of the field or the lawn? It looks really fertile, but it’s a circle. Why does this happen?”

I know, I know, I know… these look like crop circles. But if your brain went straight to aliens (like Rick Ganley’s did) I’m gonna tell you right at the top that you’re reaching for the wrong mythical explanation: it’s not aliens ... it’s fairies. 

“These rings have been appearing in lawns and pastures for millennia,” explains Peter Landschoot, an extension specialist at Penn State University. “So the lore is that there were fairies dancing around and they left the mushrooms behind.”

The rings are caused by an underground fungus that lives 3 or 4 inches under the soil. It begins growing at a central point, and then spreads outward, year-by-year. As it goes, it digests organic matter in the soil, and the by-product —  the waste produced — is nitrogen. 

If you’ve ever been to the lawn and garden center, nitrogen is the main ingredient in the fertilizers you use to green up your lawn. 

The ring is only green on the edges because as the fungus spreads its thin fingers — it’s mycelial hyphae — out in the soil, it’s active mostly on the edge, because in the center, it already ate up all that organic matter in previous years.

Ergo, a crop circle.

Where do the fairies come in?

Where things get mystical is when the conditions are right for the fungus to decide to reproduce and it sends up its sexy bits: the mushrooms. The mushrooms “appear in rings, and sometimes they will appear very quickly,” says Landschoot, who says the mushrooms can pop up overnight, or in a day or two. “And in ancient times I suppose that was something that really baffled people.”

There are somewhere in the neighborhood of 30 or so mushrooms that produce a fairy ring, and they’re native throughout Europe and North America. (And yes, foragers, some are edible. And no, I don’t know which ones. And you shouldn’t eat mushrooms unless you’re 100% sure it’s safe.) And throughout that native range there is a rich history of folklore explanations for them: portals to other worldsdancing elvesdancing buffalodragons...

Which honestly, if you didn’t have a microscope, these explanations are as good as any.

Sam Evans-Brown, is host of NHPR’s Outside/In which you can subscribe to where-ever you get your podcasts. If you’d like to submit a question you can record it as a voice memo on your smartphone and send it to oustidein@nhpr.org, OR call the hotline, 1-844-GO-OTTER, OR submit it here.

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