I have found no differences in rhizome depth behavior between contained and uncontained bamboo. Some bamboo species do have runners that go deeper than others, but that is not related to containment. Runners generally seek out heat, so typically stay closer to the surface than deep down. The only thing I have noted with contained bamboo is that it is good to have the barrier angled slightly outward, away from the plant, so that the barrier does not deflect the rhizome tip downward.

I think it depends on the thickness of the rhizome too. A 1 inch thick rhizome can grow as deep as 5-10 inches while a 1/2 inch rhizome will only grow at half the depth or often come out of the soil.

thanks, you guys....... I am debating on trying to plant INTO ground in an area bordered by concrete...and whether or not I am willing to deal with consequences dont know the variety...... maybe will post pic ?

If the concrete goes below the ground by 18-24", it will likely prevent rhizome spread. If it's just slabs and sidewalks, then the rhizomes will go under and surface on the other side...possibly many feet away. I've seen runners go as far as 30 feet laterally below the surface before sending up shoots.

I had one that was easily 40 feet before sending up a shoot. It went under a really big cedar tree, and didn't send one up till it was 10 feet past the drip line on the other side.

Your partially right. If they are not contained when young, they have no reason to send rhizome roots deep, however each bamboo rhizome has eight buds. A single bamboo rhizome rarely buds out of all eight in one season. So let's say it sends out 2 per year and each of those two puts out two per year. Underground when the oldest rhizome roots are putting out their last two buds, those new rhizomes may have no where close to shoot, so they run just under the other rhizomes until it finds an open spot to shoot. This occurs over and over again, and under the clump all of these rhizomes pleach together into a solid root mass. So each year, new rhizome buds inside the clump continue to go deeper and deeper. I remove and maintain bamboo as a hobby/job and have encountered very deep roots in clumping and running bamboo, both for the same reason.