You can loosen wet mulch with a shovel to break up slime molds.

What Is a Yellow Sticky Gooey Substance on Mulch?

by Victoria Lee Blackstone

Call the neighbors and wake the kids. You can treat them to a real-life horror show in your own backyard by letting them watch a gooey yellow blob that moves on its own across the mulch in your flower bed. Far from being a magic trick, the blob is a living organism called, fittingly, a slime mold.

About Slime Molds

Although they were formerly identified as fungi, slime molds are the primitive forerunners of fungi. They are classified as saprophytes, which are organisms that feed on dead or dying organic matter, such as wood mulch. Although you may see a slime mold on your plants, they do not harm them as a fungus might. They are capable of moving, resembling a creeping blob of dog vomit. Although that description is unsavory, it is appropriate. One slime mold's common name is dog-vomit fungus (Fuligo septica).

Habitat and Reproduction

The yellow color of many slime molds indicates the presence of spores, which is how these organisms reproduce. They prefer shady spots, particularly those that stay moist, because they can only reproduce in the presence of water. Extended periods in the sun can dry them out, which kills them. Slime molds may form in the same spot every year, but they prefer wood chips and tree stumps, both of which have decaying organic matter for them to feed on.


Yards with poor drainage and lawns with excessive thatch are attractive to slime molds. These organisms may also prosper if you use an overhead sprinkler system or if your garden is subject to frequent periods of heavy rainfall. Although slime molds are harmless, the same wet conditions that promote slime mold growth also encourage the growth of harmful fungi that may damage your plants. So if you find a slime mold, it may be an indicator of a secondary problem you should address.


Although you may not want your kids to get “slimed,” slime molds are not toxic. Chemical controls are not only unnecessary, but they are ineffective. Because slime molds are short-lived, typically lasting only a few days, the best way to control them is simply to leave them alone. If you want to get rid of them more quickly, you can disturb the yellow blob by raking through it. This allows air inside the mass, which dries the slime mold and kills it. Or, you can charge admission, sell popcorn and enjoy the show.

About the Author

Victoria Lee Blackstone is a horticulturist and a professional writer who has authored research-based scientific/technical papers, horticultural articles, and magazine and newspaper articles. After studying botany and microbiology at Clemson University, Blackstone was hired as a University of Georgia Master Gardener Coordinator. She is also a former mortgage acquisition specialist for Freddie Mac in Atlanta, GA.

Photo Credits

  • Jupiterimages/liquidlibrary/Getty Images