You will not find an answer on the record. The extension and herbarium pages that cover this yellow blob describe how the mass looks, and odor never comes up. So the question of slime mold smell sits unanswered. The common names people hang on your mulch patch point at color and shape, so take them as a picture and nothing more.
I found a foamy yellow patch on the compost pile behind the garage one wet morning in June. The mass sat on the bark chips like spilled scrambled eggs. I scraped a bit onto a stick, the crust gave way, and by the next day the whole patch had gone tan. That look is what earns dog vomit slime mold its name, and your eyes do all the work. Yours will show you the same thing when you catch a patch on your own mulch.
Michigan State University Extension describes the organism as a bright yellow mass in the scrambled egg fungus stage, which then turns tan or brown as your patch ages. Dog vomit fungus is the other label you will run into. Both names put a plate of food or a mess on your driveway in your head. Neither one says a thing about what your nose picks up when you lean over the bed. The color drains as the patch dries out, and the dull crust left behind looks nothing like the yellow that caught your eye.
Scandinavian folklore had a stranger take on the same yellow mass. People there called the stuff the vomit of troll cats, and the blob later fed the idea behind the movie The Blob. Every old name you can dig up lands in the same place. What sticks is the sight of the thing, and you can trace that pattern through the sources yourself. The troll cat story is centuries old and the movie is recent, yet both grabbed at the same yellow mess.
Your yellow patch is not a mold at all. Molds are fungi, and this thing sits in a group of its own, though the surface feels slimy when you press a finger into the crust. The blob creeps across bark mulch and turf while it eats bacteria that are working on the plant matter rotting under your beds. A patch tells you the mulch below is damp and breaking down, because that is where the food is.
Break your patch up and dry it out when the sight bothers you. I always rake the mass flat, spread the mulch thin, and let an afternoon of sun finish the job. The control here is mechanical, so you have nothing to spray and nothing to buy. Your patch can show up again after the next warm rain, and your rake handles it again in about a minute. Wet weather and thick, soggy mulch bring the mass back more often than a dry bed does.
Rake the patch apart and spread the mulch thin so it dries out. That is the control the extension pages give you, and it costs you a minute of work.
The honest answer stays put. What the record covers is how your patch looks at every stage, and the pages stay quiet on smell. Somebody will tell you the stuff reeks, and that claim about slime mold smell is not coming from the sources here. Go by the yellow mass and the tan crust that follows, because that is what the common names were built on.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
