Were they recent divisions?

Kt

You might be over or underwatering them. What variety and what are their leaves doing? More info would help.

I don't know what variety the are. Frankly, I didn't even know there were varieties when I bought them. The leaves are all dry. At the top of one, there are new tiny leaves.

Could it be replanting shock?

Far more likely you are underwatering them.

As long as bamboo is not sitting in water it is difficult to over water it.

Potted bamboo loses about half its leaves when you take it out of the ground and put it in a pot. So if it is recently potted it may just be that

Also bamboo prefers acidic water, try adding a Tablespoon of apple cider vinegar to a gallon of water when watering it.

On a terrace in NYC, when we have regularly been having temps in the upper 80's, it is impossible to be overwatering any bamboo. Your bamboo is suffering from dehydration. Sounds like it may need a bigger pot. I would transplant into a bigger container (if feasible),mulch,and shade it as much as you can for a while and increase watering until the new leaves takeover. It should recuperate!

Thanks njoasis. I'll try the vinegar for their nightly feeding. They are showing some signs of life at the top. Do you think I should cut back the dry leaves at the bottom?

Thanks everyone for your advice. The stronger bamboo is growing nicely and the runt of the litter has just started putting out tiny new shoots.