why wouldnt they be nitrogen deficient in flowering? the plants still use up N at the flowering stage of growth just not in the way it does during the vegetative stage and most flower nutes do not carry enoug N in their mix to support this leading to the yellowing of leaves as flowering progresses.They wont be nitrogen deficient in flowering. The leaves also go yellow if you have a phosphorus deficiency, but thats when more then half of your leaves go yellow. You will always have yellow leaves, most of your leaves will fall off by the time your done flowering and thats totally normal, the plant wants to put more energy into the bud at this point