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 unless contained properly. Clumping bamboo puts out rhizomes as well, but instead grows around itself, thus forming a clump. The root ball is solid like a tree and for most large clumping bamboo, the diameter of the root ball increases between two to six inches in diameter each year depending on the individual species. This growth is relentless, will break through barriers, and is very hard to manage if you're unfamiliar with this growing style. 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 chainsaw.
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 a redwood. You can see this difference makes it rather difficult to keep a privacy hedge looking nice and clean with a clumping bamboo, but it can be done. Essentially all the hedges pictured on our website use running bamboo. Regardless of what anyone says about clumping bamboo, it is quite beautiful and can make an exquisite piece in anyone's yard or garden