# Condensation or wet leaves at lights-off: likely causes and fixes

> Condensation or wet leaves at lights-off on cannabis is most often Humidity too high / VPD too low or Botrytis bud rot (grey mould). How to tell them apart, the fix for each and what recovery looks like.

Also called: water droplets on leaves at night, condensation in tent, tent walls wet, dew on plants.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=condensation

## Likely causes, most likely first

### Humidity too high / VPD too low (Likely)

- Kind: Environment; urgency: Act within a day or two
- Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids.
- Recovery: RH holds in band through lights-off for 3+ days; no new mould signs.
- Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
- Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md)

### Botrytis bud rot (grey mould) (Less likely)

- Kind: Disease; urgency: Act now
- Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading.
- Recovery: No new rot on weekly cola checks for 2 weeks.
- Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it.
- Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
- Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.