Originally Posted by echinosum

In digging them up, you will lose many of the fine roots, whcih are feeding the plant. So you need to reduce the quantity of plant they have to support, either by shortening the culms or thinning them out. If you have to do it now, not later, maybe you should just get rid of all the culms whihc have shot and not matured yet, they are probably going to abort. Although given that you have just planted them recently out of fairly small pots, maybe you can get pretty much the whole plant out, fine roots and all, if you provide it with a generous rootball, and maybe they will be barely set back at all.

Especially at this time of year, make sure they are well watered and the planting medium is rich. Include a little sand in the potting medium, as bamboo takes up silica. Put them in rather bigger pots than you took them out of in the spring.