What Is That Yellow Runny Substance on Top of My Flower Bed Mulch?

That yellow, foamy clump that suddenly appeared in your garden is probably not what it looks like.

Unappealing slime mold often grows on wet garden mulch.

That yellow, foamy clump that suddenly appeared in your garden is probably not what it looks like. Although it might appear that your dog has left evidence of a distressing illness in the flower bed, what you’re seeing is probably an organism called a slime mold, in particular a variety of slime mold called Fuligo septica. Because of its unappealing color and texture, Fuligo septica is commonly called “dog vomit fungus” or “dog vomit slime mold.”


Fuligo septica forms a wet mass that is generally foamy or slimy in texture. The mass is usually yellow, orange or cream in color and can grow to up to 2 feet in diameter. Many gardeners are horrified to discover that the slime mold is mobile, able to crawl slowly through the garden in search of food, covering plants and sometimes even climbing up walls or trees. When its environment dries, the mass dries out as well, becoming crusty and eventually disintegrating. When the dried mass is disturbed, it can release a dusty cloud of spores.

Slime Mold Biology

Although they are sometimes referred to as fungi, slime molds like Fuligo septica are actually organisms called plasmodia. The plasmodium is a formless mass of protoplasm that eats by surrounding its food and then digesting it. The moist protoplasm grows in damp environments such as wet garden mulch, rotting logs or leaf litter on the forest floor. When the environment dries, the slime mold produces small fruiting bodies that release spores. These spores germinate when the environment becomes moist again, turning into mobile cells that merge to form a new plasmodium.

Negative Effects

Aside from its appearance, Fuligo septica has no serious detrimental effect in the garden. It feeds on bacteria, fungi and decaying organic matter and does no harm to garden plants, although it can shade out or suffocate small plants that it unintentionally covers in its quest for microscopic food. Its digestion of organic matter helps in the distribution of soil nutrients, so the presence of the slime mold may actually be beneficial to garden plants that rely on those nutrients.


The growth of slime molds is not easily preventable or controllable, and gardeners who want to keep the unattractive blobs from making an appearance have little hope of succeeding. Keeping mulch from becoming excessively moist can discourage the growth of the slime mold, and once the mass has appeared, raking and aerating the environment can speed drying and the disintegration of the mass. Breaking up or disturbing the plasmodium itself, however, can spread the spores and the germinating cells, leading to more widespread growth of the organism.

About the Author

Evan Gillespie grew up working in his family's hardware and home-improvement business and is an experienced gardener. He has been writing on home, garden and design topics since 1996. His work has appeared in the South Bend Tribune, the Fort Wayne Journal-Gazette, Arts Everywhere magazine and many other publications.