Marijuana Leaves curling up after change from fluorescent to HPS



I recently switched from fluorescent lights to a 1,000-watt HPS light for my plants. My marijuana grow room is 2’ x 6’ and has more than enough ventilation. The upper leaves seem to be curling up cylindrically, but are otherwise okay. Am I doing something wrong?



Hi Cannagrow,

Marijuana plants that were grown under fluorescents and then are placed under 1,000-watt HPS lamps are generally going to have problems acclimating to the intensity of the new light. Even though these leaves are damaged, the new growth will become accustomed to the higher intensity and won’t have a problem. In the meantime, it’s a good idea to raise the light to reduce intensity and protect your marijuana plants.



The plant will be okay as new growth starts to come in.

To avoid this problem in the future, you need to “harden” the plants when moving to a more intense light.
This is done by starting the lights much higher and slowly lower the lights to the canopy over several days, or keep the fluorescents on and turn the HPS lights on for a hour one day 2 hours the next day and so on until you are on a full cycle of HPS.
It is usually easier to just adjust the height.