What is that slimy stuff in my mulch?
By Jenn Stumer – Appalachian Creations, Inc.
Every year I get questions on the peculiar looking slimy stuff that shows up in mulch. I’ve experienced it in my own mulch and have gotten used to it. But that doesn’t mean everyone else has. I typically see it more often in newer mulch, but if conditions are right, it can show up anywhere. Right conditions mean decomposing mulch with extra wetness. This season has definitely seen its share of extra rain and with it a prolific amount of slimy stuff!
The slimy stuff is actually called slime mold. Some refer to it as dog vomit fungus. Slime mold mimics the life cycle of fungi but it is not even a fungus at all. Its scientific name is Fuligo septica and it is categorized into the Kingdom Protista. Remember high school biology? There’s actually a complex reason why it is not a fungus but basically it’s because they have no cell wall in their vegetative state.
Slime mold looks like an animal got sick in the mulch. It starts out a bright yellow color in slime form then fades to a pale peach color with a thicker, pancake-like consistency. As it dries out, it turns gray and crusty then finally changes to a fine brown powdery dust. There is usually no definite shape and the slime can grow and spread out to the size of a pizza. It is not usually selective but will show up more often in new mulch (mulch that has not decomposed completely).
Slime molds do not have the ability to make their own food. They get their nutrients from decaying organic matter. Mulch is organic matter that is constantly breaking down and mixing into the soil layer underneath. The mold is feeding on the bacteria and other organisms living in the decomposing mulch and is actually important to the decomposition process in much the same way as earthworms are to the soil. It is helping to build soil and provide nutrients for the plants.
Time Frame for Slime Mold
Slime molds most often appear in spring or fall when moisture levels and temperatures are just right. I’ve also seen them show up during periods of humidity during the summer if there is a lot of moisture associated with it. Here in the Lehigh Valley, it is possible for slime mold to be found any time from April through October if conditions are right.
The Lehigh Valley is not the only place slime molds appear. They have been found at nearly every altitude and in nearly every habitat in the country and around the world. They show up in tropical rain forests, and in grasslands. They have even been found in desert areas. Sometimes they show up along the edges of disappearing snow banks.
Slime molds will not go on forever. They will eventually disappear on their own as the food source becomes exhausted and/or the environmental conditions change. Once your mulch has gone through its decomposition process, the slime mold will no longer have a food source and it will dry up. Chances are you won’t see it return again until the next wet period or you give it a new food supply of a fresh layer of mulch.
Varieties of Slime Mold
Some slime molds, if allowed to follow their life cycle without interruption (removal/conditions change), can grow a stalked structure that looks like a sphere or is popsicle-shaped. You may have seen these in your mulch as well. They resemble the reproductive organ of a male dog. These spheres are the “fruiting body” and they contain the spores. Spores are extremely resistant to unfavorable growing conditions and can stay dormant for 75 years. This makes it possible for slime mold to return year after year. Slime mold spores are triggered by moisture and humidity, so if there are any spores present, it’s a good bet they will follow the life cycle, germinate into slime mold and create the slimy moldy mess in your mulch.
Other Common Fungi found in Mulch
Do’s and Do Not’s
There is no known “treatment” for getting rid of slime mold. According to multiple internet articles I read, there are apparently no safe or legal chemical products available to use. When the slime mold shows up in your mulch, here is a short list of Do’s and Do Not’s:
- Do remove the affected mulch with a shovel, bag it and dispose of it.
- Do scrape or brush it off any affected plants.
- Do cultivate (rake) the mulch to release trapped moisture and allow for air drying.
- Do nothing and it will go away on its own after it has run its course.
- Do Not attempt to treat the area with bleach or bleach solutions. It is bad for the soil.
- Do Not spray with toxic chemicals. This can harm good organisms in the soil.
- Do Not try to wash it off. This allows the slime mold to spread more easily (by swimming).
- Do Not rake it around back into the mulch. This just spreads it around.
Rest assured, slime mold did not come with the mulch. The mulch is not contaminated. Don’t blame your landscaper or garden supply center. Spores that spawned the slime mold could have come from any number of sources in and around your area. Slime mold is not harmful to your plants even if it grows onto the plants. Also according to my research, there is no known danger to humans or animals from inhaling the spores or ingesting the organism.