I don't have any plantings in pots (other than nursery pots with plants waiting to size up to be planted in the ground), but it seems to me that at some point those pots will be full of rhizomes/roots, and you will see some indication of it by decrease in number/size of shoots, inability to keep the plant hydrated, or other symptoms.

After you divide the plant you may set it back a bit, but it's necessary I think.

Bamboo in pots should probably be divided every 3 years or so. Just un-pot it, cut it down the middle, don't mess with the roots, and re-pot. If it's particularly abundant in culms, and the root mass is good size, you can even go for 3-4 chunks.

If left in there too long it will eventually die, because it will consume all the dirt in the pot. Once that happens there is no more food. You will see the plant start declining before this happens. I had one in a half barrel for 5 years when it started to decline I took it out of the pot. The bottom 5 - 6 inches was solid roots no dirt. There was dirt there when first planted. Where was all that dirt. The bamboo has consumed it. That was crazy but true.

I've grown bamboo in both pots and in the ground. One thing about growing bamboo in pots is that you will need to keep them well watered. Also depending on the type of pot you have your bamboo in after a couple of years it may bust out of the pot. I've had bamboo grow out the side of a plastic pot before. Also some potted bamboo must be over wintered inside. A good practice i find is divide the clump every three years. I hope this helps.

Thanks for the info everyone. Very helpful.

-Brett

My best Bamboo pot is a retired fiberglass Bass Boat. Mostly filled with turkey litter, then covered with topsoil. Shoots come up like crazy. I also grow tomatoes, peppers, and bucket filled with soil on top of it all for cucecumbers. In fall i pick my crop and dig up shoots. I've found a way to use boats that can't trust to be in lake. Now neighbors r using my idea.