I was wondering what is the proper care for clumpers concerning pruning old culms and thinning out culms if disired.

I have a clump of babbusa multiplex that I planted last season, it was 3 or 4 culms and in the first growing season it has put up about 6-7 new culms about half or a little less than half as tall as the parent plant.

I was wondering when is a good time to cut down these small culms so I can have taller culms grow in their place? I don't want to take away the ability for the plant to collect energy from the sun by cutting down it's culms. I just want to have a nice semi uniform clump of bamboo.

My silverstripe also have culms that grow up and then make sideways turns, is this a normal thing for this bamboo?

THANKS in advance.