I have read some reports of various nigra forms flowering over the last couple of years, so there is at least some sporadic flowering going on for sure. I have the regular nigra form, and it is not showing any signs yet. It is still quite young though.
I seem to have had a lot of flowering. Chusquea gigantea, chusquea culeou, Phyllostachys nigra, and Phyllostachys nigra bory. I guess the price you pay when you have 31 varieties. Still seems high though.
I had a nigra that flowered about 5 years ago. Since then I have replaced it with some really nice black stuff I dug free from a local nursery.
I am working up a post with pics of my chusquea culeou that is currently flowering.
To console myself over my chusqueas, I ordered a bunch of small starts from tradewinds bamboo nursery (perfect place to order for a guy like me). They have been in the ground for a year now and some of them are really showing promise. I dug pits and buried wire mesh in a cylinder to keep burrowers out below and critters off the tops. Once established I will remove the mesh.
Henon is blooming for me here in north Oregon, but not any other nigras, including Bory, Megurochiku or black. Black is very popular here and everyone wants it. I am long since sold out of it.