A cannabis plant will and should lose some pigmentation towards the end of its life cycle. During the last weeks of flowering, growers should not be concerned about yellowing leaves on the lowest half of the plant. On the other hand, if the yellowing occurs during the vegetative stage or during the first few weeks of flowering, then your plant is suffering from chlorosis. Chlorosis, or leaf yellowing, can be induced by a variety of factors. Fortunately, there is no need to be concerned.