Yes. Slime mold goes away without any help from you, and the bright yellow blob on your mulch is already partway through its own cycle by the time you spot it. That loud stage is the start of the fruiting phase, and the color drains to tan or brown as the mass dries. Nothing you spray on it moves that along. The organism runs on a schedule set by moisture and warm weather, not by what you do with a hose or a bottle from the garden center.
Last May I pulled a loaded wheelbarrow around the corner and stopped short. There it sat on the bark, a wet yellow froth the color of scrambled egg, spread over mulch I had raked flat that morning. Eighth spring mulching that same bed. I checked it again after hauling the second load over. The froth had gone flat and dull tan around the edges, and it ended up a dry crust that crumbled between two fingers.
The mass is not eating your shrubs and it is not a disease running through the bed. That bright phase is the beginning of the fruiting state, the point where the organism quits spreading and starts making spores, and the color goes flat and brown as it dries down. Drying can also send a plasmodium the other way. Before it fruits, it draws itself into a tough survival structure called a sclerotium that sits in place until conditions turn wet again.
The color is what sends people to the search bar, because a mass that bright looks like something went wrong overnight. What follows is dull by comparison. The surface dries out, the shine goes, and the patch stops pulling your eye across the yard. So when people ask how fast slime mold disappears, the fair answer is that the bright stage is short and the dried remains sit there longer than the color does. It turns up in mulch in spring or early summer, and almost always after soaking rains.
Reaching for the hose is the common first move, and a hard blast does scatter it. The water also soaks the bark again, which is the exact condition that brought the thing out in the first place. Drying beats wetting here. If you want the show over with sooner, pull the mass apart with a rake and let sun and moving air take it from there, since a dry, broken-up mass has nowhere left to go.
Color is your progress bar. Bright yellow means the fruiting stage is fresh, and tan or brown means the mass is drying out and near the end of it.
There is one honest reason to step in. If the bed has to look presentable for guests this weekend, scoop the mass out with a shovel and carry it somewhere out of sight. Turning the top layer over with a rake does much the same job in less time. Skip the fungicide, and leave the rest of the bark where it is, because tearing a whole bed apart over one blob is wasted work on a warm Saturday.
That survival structure is why a bed that had one can have another. A sclerotium waits out a dry stretch, so a wet spring can wake the same corner of bark up again, and that is a nuisance rather than a warning about your soil or your plants. Michigan State University Extension tells homeowners the same thing. Scoop the masses if you want a tidy bed, and past that the wording is "no control warranted". The blob finishes its cycle in your mulch whether you get involved or not.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
