Cannabis leaves turn yellow for many different reasons – deficiencies, toxicities, too much light, over-watering, pests and diseases.
If you ever see your cannabis plants leaves turn a color other than green, the first thing you need to do it check your runoff. There’s a good chance the EC or pH of the root zone is either too high or too low. Trying to diagnose any leaf discoloration without checking your runoff is a step in the wrong direction. If you ever see an issue, get a baseline on your runoff EC and pH and compare it to what you are feeding on a regular basis.
If runoff is not the issue, next thing you’ll want to do is check the temperature/humidity and light intensity at the canopy level in problem areas. Poor air circulation can cause pockets of high temperatures or low humidity that will bring stress to the plants. Light intensity is another big factor that should be looked into and too much light will cause leaves to turn light green/yellow. If you’re unsure on the distance of your light, purchase an inexpensive LUX meter and use the charts below to make sure the light intensity is within a safe range.
If light or temperature is not the issue, the next thing you’ll want to do is look for insects in the growing environment. Carefully inspect underneath leaves and use a magnifying scope to look for anything moving in the substrate. If you find out that you have a pest, the plant is usually under a good amount of stress and a solution needs to be worked on quickly. At this point it’s a good idea to only remove leaves that are severely damaged. Rotate safe IPM products like insecticidal soaps, beneficial microbes and plant extracts. Hold off on pruning or thinning until the situation is under control and the plants have properly recovered.
Nutrient Disorders are another main cause of leaf discoloration. Both deficiencies and toxicities in macro and micro elements can cause leaves to change color. Some of this damage is reversible and some of it is not. If you use any of the Perfect Grower nutrient lines within recommended levels and monitor the EC and pH of your runoff, your leaves should stay green and healthy from start to finish!
Leaves can also turn yellow from root diseases and over-watering. Make sure you are allowing the substrate to dry out a little before your next watering. If you’re in soil, over-watering is easy to do and longer dry-backs are usually necessary.