A field guide to mold, bacteria and what healthy mycelium really looks like
Almost every home cultivator loses a grow to contamination at some point. The skill that separates beginners from consistent growers is catching it early and knowing the difference between a harmless cosmetic quirk and a tub you need to bag and bin. Here's how to read your jars, bags and tubs of gourmet species like oyster, shiitake and lion's mane.
Healthy mycelium is bright white and grows in fine, fuzzy or rope-like (rhizomorphic) strands that radiate outward from your inoculation points. It smells clean, faintly mushroomy or like fresh bread. As a substrate fully colonizes it may develop slight yellow or amber droplets of metabolites and a few light-blue tints on some species — both of these are normal and not contamination. The key signals are: white, consistent, advancing, and no off smell.
The most common killer. Trichoderma starts as a patch of white mycelium that looks almost normal — then turns a vivid forest green, often with a white "halo" of fuzz at the leading edge. Once it's sporulating green it spreads fast and is essentially unrecoverable. If you see any defined green patch in the substrate, do not open the container indoors; seal it, take it outside, and dispose of it to avoid spraying spores around your space.
Cobweb (a Dactylium-type mold) is wispy, grey and grows much faster and looser than mycelium — it looks exactly like spider webbing draping across the surface, where real mycelium hugs the substrate tightly. Caught very early on the casing surface it can sometimes be spot-treated with hydrogen peroxide misting, but if it's widespread, treat it like contamination.
Bacterial issues smell before they look wrong. A sour, rotten, or "baby-diaper" odor is the giveaway. In grain you'll see grey, wet, slimy patches (wet spot / Bacillus) instead of dry white growth; in substrate you may get yellow or amber slime and mushy zones. Trust your nose: a bad smell almost always means bacteria and a grow that should be discarded.
Not every odd spot is fatal — uneven colonization, metabolite droplets and minor surface bruising fool a lot of beginners. The safest habit is to photograph and date anything suspicious, note where it appeared (grain, substrate, casing) and check it 24–48 hours later. Defined green, fast grey webbing, or a sour smell means toss it. Stalled-but-white usually just needs patience and better conditions.
Tracking which contamination keeps recurring — and at which stage — is how you actually fix your process. ShroomLog lets you log each contamination event by type and stage across every grow, so you can see whether it's your sterilization, your fresh-air exchange, or your substrate moisture that needs work.
Open ShroomLog and log your grow →