My P. nigra went to seed this year also. I've heard that they all flower at the same time, wherever they are in the world. I'm in California. P. nigra is "running" so a few years ago, I noticed a new clump coming through about 10 ft from the original plant. I'm going to try to remove most of the dying culms from the old stand (the rat vector is a thing here) and attempt to germinate some of the seeds while digging and replanting the new clump nearer to the older stand to maintain some balance. Would love any info on how to germinate bamboo.
