# Sudden leaf drop over a day or two: likely causes and fixes

> Sudden leaf drop over a day or two on cannabis is most often Cold stress. How to tell them apart, the fix for each and what recovery looks like.

Also called: leaves falling off suddenly, plant dropping leaves, leaves shed overnight.

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

## Likely causes, most likely first

### Cold stress (Less likely)

- Kind: Environment; urgency: Deal with it this week
- Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported.
- Recovery: Growth resumes within a week; new leaves come in green.
- 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: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.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.