Purple/Dark Leaves? (Phosphorus Deficiency)
Cool temps or low P can cause dark, purpling leaves and slow growth.
Phosphorus deficiency cannabis? Dark/purple leaves and slow growth—see causes and analyze fast.
Common Causes
- Cold root zone
- Low P in feed
- pH out of range
- High calcium/zinc competition
How to Tell Which One You Have
Dark, sometimes purple leaves; slow growth; older leaves first.
FAQ
Cold nights?
Heat roots/canopy; cold limits P uptake.
Add more P?
Yes, within EC limits and pH 6.0–6.5.
Genetic purple vs deficiency?
Genetic purple keeps vigor; deficiency slows growth.