Trichoderma in Monotubs: How to Spot Green Mold and Stop It Coming Back

Few things sink a grow faster than opening a monotub and finding a patch of bright green. That's usually Trichoderma, the most common mold in home mushroom growing. It spreads fast, it competes directly with your mycelium, and once it sporulates it can seed the rest of your grow space.

How to recognise it

  • Early stage: a patch of bright, fluffy white growth that's denser and more brilliant than normal mycelium, often appearing suddenly.
  • Within a day or two: that patch turns pale green, then deep forest green as it releases spores.
  • Smell: some growers notice a musty or coconut-like odour.

The tricky part is the white stage, which looks a lot like healthy mycelium. If a patch looks unusually bright and grows overnight, watch it closely for a day before deciding.

Not every colour change is Trichoderma

Blue-ish bruising on mycelium where it's been touched is a natural reaction in some species and isn't mold. Mold usually forms a defined, spreading patch with a powdery surface. When in doubt, compare against photos of known contaminants and keep the tub closed while you decide.

Found it? Do this

  1. Don't open the tub indoors. Every time you lift the lid you release spores into your grow space.
  2. Take it outside, then bag it and dispose of it away from your growing area.
  3. Clean the area where the tub sat, and the tub itself if you plan to reuse it, with a disinfectant and then alcohol.
  4. Check your other tubs and jars from the same spawn batch. If the spawn was the source, its siblings are at risk too.

Trying to cut out the green patch and carry on rarely works. By the time you see green, spores are usually spread beyond what you can see.

Why it got in

Trichoderma spores are everywhere, so the question isn't whether they're present but why they won the race against your mycelium. The usual causes:

  • Contaminated spawn. If grain wasn't fully sterilized, or was inoculated in open air, the mold arrives with it. This is the most common cause.
  • Over-wet substrate. Standing water and soggy pockets weaken mycelium and favour mold and bacteria. Aim for field capacity.
  • Slow colonization. Low spawn rates or cold temperatures give contaminants time to establish.
  • Exposure at spawning. Mixing spawn into bulk in a dusty or drafty room.

Keeping it out of the next tub

  • Use a higher spawn-to-bulk ratio (1:2 or 1:3) so your mycelium colonizes fast.
  • Pasteurize bulk substrate and bring it to field capacity, not wetter.
  • Do all inoculation and spawning in a clean workspace: a still air box at minimum, or in front of a HEPA flow hood. True HEPA airflow creates a clean air shield that actively pushes contamination away from your work surface. See the Steriflo HEPA flow hood.
  • Only spawn to bulk from grain that's fully colonized with no off colours or smells.
  • Keep your growing area clean and free of old, contaminated material.

For the full picture on prep and clean technique, read Sterilization and Contamination Prevention in Mushroom Growing.

Questions? Email us at hello@gro-myco.com.

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