No...now is the worst time to try this. New bamboo shoots are highly dependent on the rhizome (root) connection to the main plant to stay alive. Ideally, you would wait for a year to ensure that the plant is well established before severing the connection. At a minimum, wait until this fall when the bamboo is starting to become more dormant. Or, take a division now from an older part of the plant.

That is the traditional thought, but after a bit of experimentation, I have an idea of why they go into shock after transplant so I tried taking 6 moso divisions (new culms)a couple days ago, and so far, they don't show any sign of shock.

Basically to minimize transplant shock, I watered the area a couple hours ahead of time, and sprayed the culms thoroughly with wilt pruf. When I took the divisions, I tried to keep as much rhizome as possible on each division, and tried to keep the original soil intact with the division. When I planted them I mixed myccorhizal powder in with my home-made potting mix.

This method has worked with fargesia nitida which is very easy to propagate, but it's still in it's experimental stage for phyllostachys species so I'll post updates on my blog if I see any progress. My prediction is that these divisions should fire off their dormant buds and make small culms this year, grow their own rhizomes, and be established after a true shooting season next year.

If you have a nice big grove that you don't mind taking a few culms from, I would say try it out.

Here is a link that might be useful: moso divisions

beachbum-
Well, now you have two answers. Take your pick and let us know how it turns out...

I have a few growing where I don't want them, so I will try transplanting them anyway now, because I would only cut them down anyway. I will try more in the fall..

Thanks everybody for the info.

I transplanted some large bamboo divisions this year. Fortunately I took the advice of this forum which was to transplant in February. Now I have almost all of my bamboo shooting and some have put out multiple shoots and roots are also going crazy. I'd wait and transplant when the time is right.

After nearly 1 week of transplanting my 6-7 week old moso bamboo new culms, they show no signs of shock, and are releafing very well, but it did require surgical precision, and very thorough preparation to get them out with this kind of success when they are at this stage in development. These culms are fully branched, but not even fully leafed out yet so this shows that it can be done. All 6 of the divisions are leafing out too.

The main reason why I'm taking them out this early is because this gives them the whole summer and fall to establish in their pots, and become very strong 5 gallon divisions by the end of the year. New shoots are likely this year since I took them without damaging the shoot buds on the rhizomes connected to these culms.

Here is a link that might be useful:

Steve: a division that doesn't have a good root system - which is the danger when digging new culms that aren't fully formed - isn't getting a "head start". During that extra time you think you're giving it the plant would much rather have been connected to the parent plant still.

BUT... I understand that sometimes you have to dig when times are not ideal, and the OP said they would cut down those culms anyway, so no harm in trying to dig. I've dug at the worst possible time too, but only when I didn't really care if I lost the division.

I would have rather dug right before shooting season which seems to give the quickest results since they are primed to shoot, but my moso was top-killed so I waited until shoots came up for my dig. Also I only wanted these 6 divisions to stabilize so they are more likely to form their own rhizome systems as soon as possible in their 5 gallon pots given that the growing season only lasts for another 3 1/2 months here.

I don't know if they are better or worse off than if I took them in the fall, but I think 6 is a good enough sample size to find out. It has been 7 days since I took them, and all of them have put out new foliage which I can tell since they don't have the wilt-pruf residue.