You can propagate bamboo by taking out sections of the spreading rhizomes. You need to have rhizome and culms (stalks with leaves). I would generally do this in April in my area. If you do it in the summer (which it still is), I would put the division in some heavy shade for a couple of weeks before it adjusts. I would not take divisions after September because I would want them to root well before the winter begins.

It's hard to say from your brief description, but I suspect that: a) you didn't get a large enough rootball, and/or 2) you dug now when the plant is growing and not dormant, and 3) you dug up some relatively new shoots that weren't well-established enough to survive on their own.

As for propagation from rhizome, it's harder than it sounds, especially for a newbie. You will have better luck with a field division done next spring that includes a decent size rootball and one or more culms.

Hello,
We have 4-5 kinds of bamboos, eatable, decorative and for furniture.
Not sure exactly what kind, Black bamboo, Giant bamboo, golden bamboo, Mexican bamboo.
What i know is that teh eatable sort is more difficult to grow. it takes a couple years before it really starts, then it is unstoppable.
As far as the giant bamboo is concerned we are now trying to get a rid of it as hard as we can. We dug up every piece of rhizome or roots we could find however it is still coming back. A real invader. Not very good for nothing. it will break after a couple years.
The Mexican bamboo though is much better. it growth like a tree instead of invading the space. The culms are so strong that it uses my blades and is hard to work, however the stuff you build with it is very sturdy.
For multiplication, we have no special precaution. Any time of the year, take a good chunk of the rizhome, put it in a large pot, water it from time to time but not too much then do not leave it too long in here, put it in the ground after 2-3 months.