Athosanswered grow question 7 years ago In the phase you are in, the stretch, the plant needs quite a lot of nutrients; while 1 or 2 affected leaves can be normal, if they issue keeps happening, it's a sign your plant needs a more strong feeding.
Withering lower leaves with dark / black patches on the edges usually is a sign of phosphorous deficiency.
Just don't go crazy for one or two leaves.