I asked that stuff because I suspected you were feeding too much. don't what the cause is to the blackening, but I know that leaves can turn black when they get too much phosphorus. the problem with growing like this is that people don't really know how much to feed or how often. many people over do the ferts as a result. canna terra pro is potting soil that has nutrients in it already. You shouldn't have to add much more, at least not for a while yet. this happens a lot too, where people buy a soil without knowing that it has fert in it already and they add more not realizing that they're killing the plant. I wonder if that's what is happening.
