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Ask Dr. Universe: Why do mushrooms grow in rings?

UPDATED: Fri., Nov. 27, 2020

Wild mushrooms sprout in the grass at Manito Park.  (Colin Mulvany/The Spokesman-Review)
Wild mushrooms sprout in the grass at Manito Park. (Colin Mulvany/The Spokesman-Review)
Washington State University

Dr. Universe: Why do mushrooms grow in rings? We have a lot of giant ones in our yard right now! – Layne, 8, Spokane

Dear Layne,

When you see a ring of mushrooms, it’s likely they are exploring for food under the ground.

Giant mushrooms in your backyard are not animals or plants. They are part of another class of living organisms called fungi. But like you and me, they need food to survive.

That’s what I found out from my friend David Wheeler, an assistant professor at Washington State University who knows a lot about fungi.

He said the mushrooms are just one part of fungi. The other part that explores the soil for food actually lives under the soil.

This part is called the mycelium and looks a bit like cobwebs or stretched-out cotton candy.

Mycelium help the fungi explore different spaces and absorb nutrients from things like dead logs or decaying leaves.

Wheeler said we might think about the way a mushroom ring forms, including how the mycelium spreads out, as if it were a ripple in a pond.

Just as a ripple starts with a raindrop or stone, a mushroom ring begins with a tiny spore.

To help grow new fungi, mushrooms will release spores, which are like seeds. After a mushroom releases the spores, they float through the air, and when they land in soil, the mycelium begins to grow beneath it.

It starts expanding outward from the place where the spore landed. This allows the fungi to cover a lot of ground on the hunt for food.

It’s at the outer edge of the mycelium where we see the ring of mushrooms grow up from the soil.

I found out there are mushroom rings that have been around for a really long time. For instance, one mushroom ring in France has been around almost 700 years.

As the fungi spread out in search of food, the ring got wider and wider. Now, the ring is almost a half mile wide. You would have to walk the length of eight football fields to get from one side to the other.

Even though fungi don’t have legs, they sure know how to go the distance. And a big part of that has to do with their mycelium.

“Every step you take in the forest, under one foot – even one kid foot – there could be lots of cells of mycelium,” Wheeler said.

Wheeler also told me that fungi sometimes compete for food. If you look at the mushroom ring in your backyard, you might notice something unusual about the grass around it.

Sometimes grass inside the ring might be brown, and the grass outside the ring might be bright green. That’s because fungi and grass both like to eat the same thing.

They are both after the nutrients in the soil. But as the fungi grow, they can steal away nutrients faster than the grass can handle.

It’s great to hear you are observing nature in your own backyard. It’s a good reminder that we can find science questions almost anywhere in this big, wide world – even in a ring of mushrooms.

Sincerely,

Dr. Universe

Ask Dr. Universe is a project from Washington State University. Submit a question at askdruniverse.wsu.edu.

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