hmm. I honestly don't even remember it's been so long. the ones I'm trying to get shoots from I just moved because they were close to objects and knew they wouldn't spawn but now I want more so I moved them and nothing is growing. So that's probably the issue. I'll have to try and find some shoots. thanks for the tip!
I'm pretty sure bamboo only produces shoots once, when it goes from not-fully-grown to fully-grown. They don't keep producing more like in New Leaf. If you want lots of shoots, or just lots of bamboo, I think the best way is to use NMT until you get the bamboo island. It's fairly a common island to appear, in my experience.
Bamboo trees only spawn shoots one time in this game. Each bamboo tree will produce one or two bamboo shoots, and that’s it. If you want more shoots, you need to plant one and grow a new tree. I like it much better this way! I could never have bamboo in my town in New Leaf because it would just grow out of control.