Answer: Otatea acuminata aztecorum (Mexican Weeping Bamboo) reaches about 20' in height in its native habitat but will only reach 12'-15' in your southern California garden. It is a clumping rather than a running bamboo. As such, the clump will continue to expand as the plant matures. The root system will be concentrated in the top 12" of soil. Otatea does not have a reputation for being an invasive nightmare, but if you're concerned about keeping the plant under control, I'd suggest planting in a large container and burying the container in the ground. This way you can unpot and divide the plant, and keep the clump small.
Q&A Library Searching Tips