Posted: 06/09/2012 at 21:37
I think Bronnie makes a good suggestion about thinning the weakest stems of the plant. We had a well established Phyllostachys Nigra plant that had to be moved due to building work, when it was replanted in its permanent home it sulked for a whole season, at least, and threw up some very pathetic canes. I made sure it had as close to ideal conditions as possible (as you have done) and pruned out the most spindly stems as the emerged and kept any slighty thicker ones. This summer (3 years later) it has had its best year yet and I have gone back to stripping the leaves off the lower half of the canes to reveal the black stems. I think you may have to be very patient - maybe they don't like being transplanted?!