Short answer
If buds in a curing jar have gone mouldy, throw them away. Don't trim around the mould and don't smoke them. Then check every other jar, and dry the clean buds until a sealed sample reads a stable 55–65% RH (water activity 0.55–0.65). Established: mouldy flower isn't safe to smoke, vape or extract.
Why
Mouldy cannabis can carry spores and mycotoxin-producing fungi, which is why regulated markets test flower for yeast and mould [1].
Mould grows when the bud's water activity is too high. ASTM sets 0.55–0.65 aw as the safe range for dried flower, and says flower above 0.68 needs more drying [2][3]. A jar holds in whatever moisture is still in the bud cores.
Botrytis can also come in from the plant. It rots dense colas from the inside, often before anything shows, when late-flower humidity is high or water condenses at lights-off [4]. Buds infected that way can rot in the jar even when the dry looked right.
The numbers
| Reading | Meaning | Action |
|---|---|---|
| Sealed jar, stable 55–65% RH | aw 0.55–0.65, safe [2] | Keep curing |
| 65–68% RH | Borderline | Take the buds out and dry them more |
| > 68% RH, or 75%+ overnight | Too wet [3] | Dry them now and watch for mould |
| Fuzz, grey dust, brown core | Mould | Throw it away |
What to do
- Wear a mask and gloves. Bag the mouldy buds where they sit so the spores don't spread.
- Throw out every bud with fuzz, dust, a brown core or a musty smell, and every bud that touched one.
- Open every jar. Break open the largest buds and check the cores.
- Spread the clean buds on a screen at 15–21 °C (60–70 °F) and 55–62% RH until the small stems snap.
- Re-jar them in clean jars, about ¾ full. Read the hygrometer only after 12–24 hours sealed.
- Wash the old jars with hot soapy water and dry them fully.
Common mistakes
- Trimming off the fuzzy bit and keeping the bud.
- Jarring buds by feel, without a sealed hygrometer test.
- Packing jars tight.
- Leaving a jar unopened for weeks early in the cure.
Related
- Full article: Botrytis (bud rot / grey mould)
- Answers: ammonia smell in jars · how full to fill jars
- Articles: curing and burping · drying
- Terms: botrytis · water activity · mycotoxins
