Here in 8b, it took over 10 years for my Al Karr to spread 5 feet across. You shouldn't need a barrier unless you want the roots kept away from underground pipes or other possibly delicate items that you might want to dig around later.

The rhizomes should be no problem since they only spread a few inches at most, in one year.

I would not use a barrier since the plant needs room for the roots to grow, and to make a healthy and beautiful plant. Barriers are mainly for runners and are installed to stop rhizome spread.

Kt

I guess it depends on how often you want to dig and check up on the bamboo. If Al Karr spreads effectively in the next two years for you and it is near pipes or concrete...do you want to dig it up and check all the time? I would install a barrier just because I wouldn't want to worry about it.

Here is a link that might be useful: Barrier install information

I agree completely with kentuck. There is no need for barrier with clumpers in general and this one in particular. Bamboo -- even aggressive runners -- do not break concrete, and they do not damage or invade pipes, sewers, or drains.

Kudzu is right. Alphonse Karr is a small species of bamboo as all the multiplex are. If they got under concrete, they couldn't do anything. Also, the multiplex species is a tight clumper, meaning it spreads very slowly and very easy to control. Warning:Don't plant bamboo close to the pool, unless you don't mind cleaning the leaves out of the filter constantly. Today I removed an entire clump of bamboo from a property because of the problems with leaves in the pool. The pool was twenty feet away from a mature clump of wamin buddha belly, which coincidently grows to the same height as Alphonse Karr. I recommend another multiplex called golden goddess, not to be confused with chinese goddess. It grows to about 10-12 feet which is plenty high for privacy.