Rhizomes are the part of the root system that go exploring for new territory. Building a small trench where you want to corral your bamboo will help maintain the ability to find these Rhizomes as they seek new ground, and trim them as needed. The reason we fill this trench with sand as opposed to other materials is simply how easy it is to take back & then replace.
We do not necessarily recommend trying to create nutrient or fertilizer deficiencies in order to control the growth of your bamboo. This practice can backfire in multiple ways, where your bamboo might fight for life and grow at an eccentric rate, or look sick & eventually die. Neither of which are good options.
San Franciscians can pretty much plant bamboo year round where as the surrounding areas may have to wait for spring (ideally) or fall (weather permitting).