It depends. I know people who have had lucky bamboo in the same container for 5 years. As with most plants as long as the roots have sufficient room the plant will be find in its original container. However if the height of the plant causes a stability problem, you will need to either repot it or cut the top out of the lucky bamboo. You can root the tops and create new plants. You can also root prune the lucky bamboo if you need to. Our Caring for Lucky Bamboo page and our Caring for Lucky Bamboo Newsletter will give you a few pointers.