Picture of the Week

June 5, 2023

What's Growing On My Mulch​?

Tom Creswell, Plant and Pest Diagnostic Lab Director, Purdue University

When rains are frequent, moisture dependent slime molds often make an appearance on mulch. Slime molds develop rapidly and change color and texture over time; usually going from shiny and brightly colored, to powdery and gray or brown as they mature and get ready to release powdery spores which blow to new locations.


Slime molds get their nutrients from bacteria and small bits of organic matter which is why it is common to see them growing on mulch. Although slime molds may grow up onto nearby plants, like turf or vegetable in the garden, they do not harm plants. After several days of dry weather slime molds will usually be less noticeable. If you want to speed this process, you may rake the mulch or affected areas of the lawn to promote air drying. However, slime molds will fade in time without any action on your part, and will usually return with the rain.

Click Images to enlarge

slim mold on mulch Figure 1. Slime mold growing on mulch
slime mold on turf Figure 2. Gray colored slime mold growing on turf
slime mold on turf Figure 3. Gray colored slime mold growing on turf
slime mold on onion Figure 4. Slime mold in the garden on onion.
slime mold on lettuce Figure 5. Slime mold in the garden on lettuce.