When Your Substrate Goes Wrong
When Your Substrate Goes Wrong
Almost every failed grow traces back to one of five things: contamination, moisture, temperature, a missing casing layer, or fruiting conditions. This page sorts symptoms into causes.
If you're mid-panic, start with the symptom that matches.
Green, black or pink mould
Green almost always means Trichoderma, and by the time you can see it the colony is far larger than the visible patch. It usually indicates under-sterilised substrate, a contaminated spawn source, or supplementation without adequate sterilisation.
The reliable fix is upstream. Home sterilisation is where most contamination originates — not from technique, but from equipment that can't hold temperature and pressure long enough. Our grain jars and grain bags are pressure-processed and sealed, so the batch starts clean.
Colonisation stalled partway
Mycelium ran, then stopped in a ring. Usually anaerobic conditions in the centre — too wet, too densely packed, or not enough gas exchange.
Fully colonised, nothing fruiting
Two common causes. For Agaricus — button, cremini, portobello — it's a missing casing layer. They will not pin without one, no matter how perfect the substrate. For everything else it's usually fruiting conditions: humidity, fresh air exchange, light or temperature.
Sour smell or slimy patches
Bacterial contamination, and it means too much water. Wet spots go anaerobic and bacteria take over. Not recoverable — the batch is finished.
Target moisture by substrate type
Substrate discolouring or drying out
Is it worth saving?
Usually not. Trichoderma spreads through a block faster than it shows on the surface, and a contaminated batch next to clean ones puts the clean ones at risk. Cut your losses, clean the space, and start from sterile.
Preventing the next one
Or remove the variable entirely — substrate that arrives sterile, hydrated and pH-buffered.