well, it depends on the type of bamboo. Some varieties shoot
  runners - they're the ones to watch out for. But most varieties
  of bamboo that are sold stay in CLUSTERS, so you'll know that
  one bamboo will spread to about 5/6 feet wide at most and then
  stop. I forget all the different types - but I could never
  convince anybody that we should get some - just because of the
  horror stories folks have about the WRONG kind of bamboo. My
  favorite is the ones that grow to 40 feet tall and you cna build
  houses out of. That stuff is amazing. "