Unfortunately the classification running and clumping is deceiving. All bamboo spreads. Running bamboo sends rhizomes wandering around, and they may put up shoots anyplace they go. They must be contained. Clumping bamboo puts out rhizomes as well, but depending on the species a fixed distance away from the original plant. The root ball is solid like a tree and for most large clumping bamboo, the diameter of the root ball increases between one and two feet per year. This growth is relentless, and will break through barriers and is very hard to manage. After ten years, a 25 gallon Bambusa may well be 20 feet in diameter at the base, and spread to over 60 feet at the crown. (see picture). The center will be dead canes and thatch, and be impossible to get near without a chain saw.
The other big difference between running and clumping is the form. Most runners are upright, and remain manageable within the contained space in which they grow. Clumpers naturally lean out from the center forming a wonderful area of shade, although some lean over all the way to the ground. It is like the difference between a live oak tree and redwood. You can see this difference makes it very hard to keep a privacy hedge looking good with a clumping bamboo, but it can be done. Essentially all the hedges pictured on our web site use running bamboo. On the other hand, as a specimen, clumping bamboo is amazing.