Yes. That yellow crust on your mulch is a sign the bed is alive, not a sign of trouble. The slime mold garden benefits come down to what it eats. It grazes the bacteria that feed on decomposing plant matter, so it only turns up where your mulch or leaf litter has already started to break down. Nematodes and beetles then eat the mold, which drops it right into the soil life you spend money trying to build.
The best soil in my own yard sits under a mulch path where a slime mold comes back every July. I pulled that layer back one afternoon and found worm castings through the top inch (2.5 cm) and fine roots running sideways into the damp litter. That strip gets no fertilizer and no digging. The blob had been grazing bacteria in there for a week or more, and something had already eaten a notch out of one edge of it.
Call it a slime mold decomposer if you want, though the mold never touches your wood chips. What it eats is the film of life sitting on that dead material, mostly bacteria, along with fungal spores and maybe a few small protozoa. Michigan State University Extension calls the mold saprophytic, which is a long way of saying the thing lives on dead stuff and leaves your plants alone. So you have a grazer one step above the fungi doing the real rotting, and one step below the animals that come for it.
A slime mold gathers a thin scatter of bacteria into one visible mass, and that mass is easy food for the beetles and nematodes hunting through your mulch. You cannot see any of that from the top. You see a blob. What your bed has is a busy layer of decay with a grazer sitting on it, and a few predators working the grazer.
The one real cost shows up when the mass climbs off your mulch and onto a plant. Slime molds use leaves and stems as a surface, and a crust parked on a leaf blocks the sunlight that leaf needs. The tissue underneath turns yellow while the blob sits there. No spray fixes that, because the mold is not feeding on your plant at all. Break the mass up with a stick and your leaf gets its light back.
You get more out of the slime mold food web by leaving the blob where it is. Every crust you scrape off is bacteria that goes ungrazed and a meal that the predators in your mulch never get. So leave it alone unless it is shading a plant, and look at the bed again in a few days. Rake it into the mulch if the look bothers you, and skip the fungicide, which does nothing here.
UW-Madison Division of Extension offers a third option beyond leaving it or removing it. Take a hand lens out to the mulch and watch the mold up close, or grow one indoors as a science project with a kid. It costs you nothing, and your bed keeps its cleanup crew.
Judge the mold by where it sat, not by how it looked on the day you found it. A blob on bare mulch tells you the chips underneath are breaking down and feeding something, which is the whole reason you spread them. A blob on your hosta is a shading problem. Ten seconds with a stick clears it. Neither one is a plant disease, so nothing on the fungicide shelf has a job in your garden today.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
