taralynna-
If you're sure it's a clumping bamboo, the barrier is a totally unnecessary waste of time and money, and may even interfere with the healthy growth of the bamboo over time. It will not pop up in their yard. The nature of a clumping bamboo is to stay in one place and get a little bigger in diameter each year. It will never send out runners like a running bamboo. Unless you plant this on the property line, it will never get big enough in your lifetime to bother your neighbors. What species are you planning to plant?

The block wall is on the property line and I'm planting it along the wall. There are some gaps in the mortar and I am not sure how deep the footings are in some spots, which is how the other bamboo came under, I believe.

I don't know what I'm going to plant. I'm doing a Japanese Garden and I need the clumping bamboo to look Japanese, and be about 15' tall (Southern California). I haven't quite figured out which bamboo to use. I'm open to suggestions if you have any.

If it's a clumper, the defects in the wall/footings are not an issue in terms of it crossing over. A clumper will have a root system that looks like a large donut that gets bigger in diameter each year...no satellite roots will be sent out. If/when it expands to the wall, it will most likely flatten up against it, but not deform it. The wall will act as a barrier and won't be penetrated.

When you say a bamboo should look "Japanese," what are those characteristics: Fully erect vs. a weeping habit? Large leaves or tiny leaves? Skinny culms or fatter culms? Green culms or yellow culms or striped culms? Etc.

Kudzu, thanks for the info on the clumping bamboo, I understand now. You saved me a bunch of money on a root barrier I did not need :-) thanks.

Characteristics of the bamboo I would like: Erect, small to medium leaves, skinny or medium culms with leaves from the bottom to the top (I don't like the bamboo that are stocks at the bottom and leaves at the top). Green, yellow or striped are good. The height is important at 12-15'. We have high winds and hot temps. Winter can bring hail but not snow (32 degrees here and there).

taralynna-
There are a number of clumpers that would work for you with those characteristics. The two that I thought of first are: Borinda augustissima or Bambusa multiplex, which should not be too hard to find. Below is a link to a web site where you can look at photos of these. If you click on a thumbnail, it will also display the physical characteristics like: amount of sun exposure, max. height, hardiness rating, etc.

Here is a link that might be useful: BambooWeb photos

I have Bambusa Oldhamii and Vulgaris and have seen tremendously dense roots spreading 10' or so away from clump, and they seem to be starving other plants of water, etc.

I wish I had a root barrier.