MistaOCanswered grow question 2mo ago If a male cannabis plant shows yellowing at the tips of the upper leaves along with a purple stem, it’s less likely to be a nitrogen deficiency, which usually starts in the lower leaves. This pattern could point more toward a pH imbalance, nutrient lockout, or even overwatering. Measuring the pH of both the water and, if possible, the soil should be the first step. A purple stem can also result from phosphorus deficiency or cold temperatures. In some cases, the purple color is genetic and harmless. Make sure the plant isn’t being overwatered and is receiving the right amount of nutrients—not too little, and not too much.