Here’s what to know about mushrooms popping up all over the city

With heavy rains, mushrooms have been popping up in mulch, garden beds and lawns all around Colorado. But they don’t stick around too long. It’s like the obscure ’90s Dada song, “Here Today, Gone Tomorrow.”

Mushrooms’ popularity has risen over the last few years with most gardening forums saying that they are a sign of healthy soil. The next common reaction, though, is advice to remove them before your dog, cat or children eat them.

Here’s what to know about the fungus among us.

What to make of Colorado’s fungi?

Jon Sommer, president of the Colorado Mycological Society, said that these urban fruits vary from the ones of Colorado’s forested areas in lifestyle, context and purpose. Generally, mushrooms can be saprophytic, parasitic or symbiotic. Most of the ones found in Denver area gardens and yards are saprophytic mushrooms, meaning they are our decomposers. The ones in that category we are most familiar with here are morels, oyster, turkey tail, and puffballs.

But the decomposing mushrooms in your yard are not for eating. While Sommer said that Colorado has very few truly toxic mushrooms and none of the deadly ones, it’s best to avoid eating them without accurate identification.

There are many common decomposers in Colorado gardens and lawns, but a few have popped up on gardening forums and in yards this year. The Parasola plicatilis (Japanese umbrella) is very short-lived and looks like little umbrellas. The Marasmius oreades (fairy ring or Scotch bonnet) are common to fields and lawns. Its name can cause confusion, since many other mushrooms grow in a ring pattern. The Coprinellus micaceus (mica cap) is common in urban areas under trees and woody areas in lower elevations along the Front Range. The Phallus impudicus (stinkhorns) may be confused as a morel by beginners but you know them from their bad smell, which attracts flies for spore spreading.

The forest mushrooms tend to be more symbiotic with woody plants and trees, meaning they have a mutually beneficial relationship with each other. In other words: no mushrooms, no trees. A fun read about how fungi are the connectors of our world is Merlin Sheldrake’s “Entangled Life: How Fungi Make our Worlds, Change our Minds, & Shape our Futures” (Random House). Or, to learn more about identifying the edible ones, read “Mushrooms of the Rocky Mountain Region” (Timber Press) or “The Essential Guide to Rocky Mountain Mushrooms by Habitat” (The University of Illinois Press).

On a zombie note (for fans of the series “Last of Us”): If the idea of parasitic mushrooms excite you, check out an upcoming free workshop with guest speaker Dr. Alisha Quandt, who researches fungi that take over insects. This event is sponsored by the CMS at Sturm Auditorium at the Denver Botanic Gardens on June 12, from 7 to 9 p.m.

Why are decomposing mushrooms growing here?

Most of our urban mushrooms are decomposers. They love wood mulch. Many are found in grassy or mulch areas breaking down organic material. As mulch is a common garden and yard filler, it will contain fungi from the area in which it was harvested. The mulch you bring in comes with its own fungus. If your mulch is from oaks, elms, ash or aspens, you may find yourself lucky with morels, or that chopped-down cottonwood may surprise you with oyster mushrooms.

Finer mulch pieces will all decompose faster, thereby inviting fungi. Composting the mulch in advance of spreading it out can help heat and kill fungal spores, although that’s not always effective. Mulch from mature softwoods like pine or cypress are more rot-resistant due to lignin, wax and protected cellulose. This combination in mature trees makes their mulch less hospitable to our friendly fungal decomposers. However, young softwood trees  lack these protections so they break down more quickly. That said, wood mulch is still preferred over rock mulch since it does break down and contribute to soil health.

If you find mushrooms growing in a grassy area, chances are it is a sign of organic material being decomposed. Should they persist well beyond our rainy cool season, you may have a leak or shady area that needs drying out.

The good news is that fungi colonization and fruiting prefer wet and cool weather. Our cool, wet rains of spring will come to an end and mushrooms will dry up quickly as the Colorado sun comes out.

Should you get rid of them?

You really cannot get rid of them. You could remove the top soil layers but chances are what you fill in with will have spores. Of course, you can remove the fruiting bodies (mushrooms) by picking them. If you want to slow down their spread, remove the fruiting bodies before the gills open and release airborne spores.

But mushrooms’ network of mycelium will continue growing underground, doing their decomposing business. This is a good thing, since fungi are critical to the carbon cycle by sequestering carbon and distributing the recycled nutrients back through the soil via their hyphae.

Contrary to what some websites say, these decomposing mushrooms are not harmful or a nuisance. Avoid sprinkling any type of fungicide on them as they are impossible to fully kill and that will only damage the local ecosystem.

Besides, mushrooms are not damaging the plants growing in your yard and garden. They also are not likely symbiotic to your annual plants. The mycelium, though, still increases the availability of soil nutrients, which can be of benefit to the garden.

If you are interested in learning more about all types of mushrooms, check out the Colorado Mycological Society. It has been around for 57 years in Denver offering field trips, courses and community. CMS has more than 1,300 members, people who are interested in mushrooms for all types of reasons: food, medicine, compost, identification and general geeking out on how cool mushrooms are.

Ultimately, mushrooms are a necessary part of our ecosystem. During Colorado’s wet seasons, bask in their beauty as they fruit above ground, ever so temporarily.

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