Bamboo will grow in any direction that has desireable growing conditions.

I've transplanted black bamboo(P. nigra) at all times of the year with success, but the big trick to that is to get enough rootball around the culms(s).

Best times for success in transplanting are in early Spring or late Fall, or when the plant is dormant(Winter).

During transplanting, do NOT let the rootball dry out before replanting. I think that is the most common reason for losing a transplant. After re-planting, keep watered well.

Kt

I'd like to expand on thing in kentuck's excellent answer. Bamboo is not like other plants: new shoots are too fragile to survive. They do not have a significant root structure, and severing the connection to the main plant is like cutting an umbilical cord. You generally only have luck with a division surviving if you select a mature, fully-leafed out culm with adequate root mass. If I'm doing a division, I typically select a chunk with one or more culms that are at least a year old, and on average I take a root ball about the size of a soccer ball.

The other thing to note is that the bamboo you planted could also have grown straight under the fence into your neighbor's yard (or whatever is over there). Besides upsetting neighbors, it's also one of the reasons bamboo has such a bad reputation with many people.

You should take steps to avoid this with either rhizome barrier or rhizome pruning a few times each year. The rhizomes of running bamboos can extend much farther than the shoots indicate.