I'm pretty careful about ChatGPT but I "chatted" with this question:
"What are some of the reasons for the leaves of a cannabis plant drooping at the end of the photoperiod?"
I'd thought it was mainly a turgor issue with light coming in at second place but there could be a variety of issues. What throws me off about blaming PPFD is that I grow plants at DLI's of 70-80 and haven't seen leaves droop. I grow in hydro with temps in the low to mid-80's (in veg).
It "might could" be a combination of factors, I'm thinking.
The text below is from an AI agent.
Note that there are no references.
Drooping cannabis leaves at the end of the photoperiod (especially in the light cycle of a 12/12 or 18/6 schedule) are usually
not a cause for concern—in fact, they often reflect
normal circadian behavior. However, several factors can contribute, ranging from natural rhythms to environmental stress. Here's a breakdown:
1. Circadian Rhythms
- Plants droop naturally toward the end of their light cycle as part of their internal clock.
- This is more pronounced in healthy, vigorous plants and typically resolves shortly after lights come back on.
- Similar to how humans wind down at night.
If drooping is
excessive,
progressively worse, or
lingers after lights on, consider these:
2. Overwatering
- Roots stay too wet and oxygen-deprived.
- Leaves droop and feel limp.
- Gets worse over time, not just at lights-off.
3. Underwatering
- Lack of water leads to cell turgor loss.
- Leaves droop and may feel dry or papery.
- Recovers quickly after watering if this is the cause.
4. Root Zone Temperature
- Roots too cold (<65°F) can reduce uptake and cause droop.
- Roots too hot (>75–77°F in hydro) may cause oxygen depletion.
5. Heat or Light Stress
- High PPFD (light intensity) or canopy temperatures (>85°F) can stress plants by day.
- Leaves may droop toward end of photoperiod due to cumulative fatigue.
6. Nutrient Stress / Salt Buildup
- High EC can reduce water uptake through osmotic resistance.
- In hydro, poor balance or too frequent feedings can cause this.
7. VPD Issues
- Low humidity or high temps = high VPD → too much transpiration.
- Plant may "close down" and droop to reduce water loss.
What to Check
- Do they perk back up within 1–2 hours of lights on? Normal.
- Do they stay droopy during lights on? Problem.
- Do pots feel heavy or light? Check for over/underwatering.
- Leaf feel: Limp and wet (overwatering) vs. dry and floppy (underwatering).
- Look at root zone temps and light levels. Adjust if excessive.
Let me know your grow setup (media, watering schedule, EC, light intensity, etc.) and I can give you a more tailored diagnosis.