Heelebore-
I'm sorry to tell you this, but propagation from culms only works with some tropical bamboo, which you probably don't have since your "My Page" says Canada. What species is this? Where did you hear about this technique? Typically with the bamboo that grow in northern climates, you can only propagate by rhizome division.
In addition, I've never seen topping a bamboo damage it in any way, so something else must be happening if the remaining plant is dying.
Can you provide some more details and/or post some pictures?