Garden Dilemmas, Delights & Discoveries, Ask Mary Stone, New Jersey Garden blog

Fixing Funky Fungi in Mulch

A variegated shrub with a colony of beige mushrooms in mulch underneath.

Hello, fellow lovers of all things green. It’s mulch time, and John from Andover, NJ, asked what kind of mulch to use. First and foremost, stay clear of trunks and stems to prevent disease. That’s my polite way of saying no volcano mulch, please. To avoid mushrooms in the garden, choose a quality mulch and apply it correctly. But if impacted, there are ways of fixing funky fungi that can grow in mulch. Here’s how:

Choosing the Best Mulch
An office building with mulch piled around a birch tree resembling a volcano.

Please Stop Mulch Volcanos

There once was a trend and using Cocoa Mulch, which can be toxic to pets, and the sweet smell can attract wild animals, so best to stay clear. Then there’s the controversial Dyed Mulch, often made from recycled wood products such as wood pellets, old decks, and other construction debris, which may have harmful chemicals. Then there’s the dye they use to camouflage the wood. Hence, Dyed Mulch is another stay-away to keep plants healthy. Recall how hot it is to walk barefoot on a blacktop driveway. The same goes for Black Mulch around plants, impacting plant health by heating the roots.

I prefer Cedar and Hemlock mulch, which have fewer mold spores than other hardwood mulches and don’t break down as quickly. Leaf mold makes a fabulous mulch, as discussed in Leaf Mold—Better than Mulch.

Jeanne’s Fungi Dilemma 

Speaking of spores, Jeanne shared a fungi dilemma, an alien-looking plethora of mushrooms amongst her garden mulch. Mushrooms are the fruit of valuable spores that decay organic material and recycle nutrients back into the soil, which is beneficial for plants. However, in volumes, they’re unsightly in the garden. The good news is most mushrooms are not toxic and do not cause disease, though a few are poisonous if eaten, so keep curious critters and kids away.

Cream colored slime mold on mulch

Slime Mold looks like a dog hurled (sorry if you’re eating breakfast)

A variegated shrub with a colony of beige mushrooms in mulch underneath.

Mushrooms are good for our earth but unsightly in the garden.

Many types of mushrooms can evolve in your mulch, from the classic toadstool to smelly fingerlike stinkhorns that attract insects. There are the puff balls I loved to pounce as a kid to release black clouds of spores. Then there’s the bright pink, orange, or yellow slime mold that looks like a dog hurled. Sorry if you’re eating breakfast.

Groups of birds’ nests mushrooms look like little eggs inside cups. It’s the dreaded artillery fungus with clusters of minute orange-brown or cream cups with black specks in the center, which shoot tarlike spores onto siding, walkways, and even on cars that are impossible to remove.

How to Prevent Mushrooms in Mulch

Mulch should never be more than two or three inches, as too much inhibits air circulation needed for root health. Plus, too-thick mulch will create a mat that hinders moisture from getting through to roots, and it kills microorganisms that prevent spores from fruiting, meaning you’ll have more mushrooms. Moisture, cold temperatures, and shade provide an ideal environment for mushrooms.

Hand watering at the roots or drip irrigation rather than sprinklers will help limit mushroom colonies. While fungicides are used in lawns to treat short-lived fungi like leaf spot and root rot, they won’t help fungi that create mushrooms. Instead, rake mulch periodically to interrupt the fungal cycle, inhibiting them from fruiting. If mushrooms have formed, remove them and toss them into a bag to dispose of them to prevent further spreading of spores.

Black mulch with three cream shaped mushrooms with grey edges.

Too thick mulch encourages mushroom growth.

Mushrooms prefer acidic soil. Adding lime can make the soil more alkaline, but it would negatively affect other acid-loving plants. (Many folks apply lime routinely: please don’t without testing the soil first, which you can do at your local extension office.)

How to Fix Funky Fungi Dilemmas in Mulch

They say two tablespoons of baking soda mixed with a gallon of water won’t change the soil’s chemistry or pH, but it will disrupt the ideal conditions for fungal growth.

While you can refresh decaying mulch by adding a half-inch of fresh mulch on top, once mushrooms become running amok, it’s time to remove and install new mulch. Add the old mulch to the compost pile, turning it every few months to create compost soil.

Organic compost soil (or leaf mold) instead of mulch is a nourishing alternative for your plants. It’s already broken down, so mushrooms won’t have much to feed on. Penn State researchers discovered blending four parts of mushroom compost, also sold as mushroom soil, with ten parts of mulch significantly impedes artillery fungus and other annoying fungi because it contains beneficial microbes that destroy it. Plus, mushroom soil, the byproduct of edible mushroom production, will boost plant growth. If you can’t beat em, join em.

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Mary Stone, owner of Stone Associates Landscape Design & Consulting. As a Landscape Designer, I am grateful for the joy of helping others beautify their surroundings which often leads to sharing encouragement and life experiences. These relationships inspired my weekly column published in THE PRESS, 'Garden Dilemmas? Ask Mary', began in 2012. I dream of growing the evolving community of readers into an interactive forum to share encouragement and support in Garden and Personal Recoveries - seeking nature’s inspirations, stimulating growth, weeding undesirables, embracing the unexpected. Thank you for visiting! Mary

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