What are Those Yellow Blobs Growing on my Wood Chips?

Have you ever walked out to your wine cap bed expecting to find wine cap and instead found something resembling dog vomit? Well, you're not alone. Let's talk!

yellow slime mold growing on wood chips
yellow slime mold growing on an old log
yellow blob slime mold growing on wood chips

What is the yellow stuff growing on my wood chips?

This nifty organism is called Fuligo septica. Dog vomit slime molds, to the untrained eye, look very like dog or cat vomit. In fact, Scandinavian folklore identified this organism as the vomit of troll cats, "witches butter", or spit of spirits. This slime mold is very common, and we see it occasionally on wine cap beds and sometimes on the bark of nearly spent hardwood shiitake logs.

Will dog vomit slime mold harm my Wine Cap bed?

Alarming as it looks, this particular slime mold is not harmful to the mushrooms we are growing. Slime molds themselves are not competing for the same food that our mushrooms eat. Slime molds are actually feeding on bacteria and tiny microorganisms associated with decay, thriving in late spring and early summer when moisture is usually prevalent on wood chip beds and mulches, or occasionally on the surface of older mushroom logs.

This slime mold creeps along as an egg-white-like sticky slime, consuming available microbes and bubbling up in the yellow mass that eventually produces spores before finally crusting over and crumbling away. Many people first notice this in wine cap beds and panic. The best thing to do is to back off on watering (slime molds love moisture)  and avert your eyes. Many people tell us weeks after the first panic attack that they are harvesting more mushrooms than they can eat off these slime mold inhabited beds.


Yellow to dark yellow blob-structures that eventually harden over time
Caused primarily by:
Excessive heat and/or overwatering
Typically seen in late spring to early summer
Is it harmful?
Typically not. Slime molds do not compete for any of the same nutrition that Wine Cap or Shiitake need.