first year = no trim. when it's time to trim, you should try to remove the shoot as close to the rhizome as possible. "why"? because the portion that remains 'un-trimmed' will basically turn into a rhizome (an underground stem containing shoots which have the ability to produce new plants). so now you have an untrimmed shoot that will develop at least one ring of buds that will produce say 6 new shoots next spring. if you have 'trimmed' 10 shoots back this year, what will you have next year. 6 x 10 = 60 shoots. this does not take into account the new shoots to be produced from the original rhizome. believe me, if they are growing in half way decent conditions, by your 4th of 5th year you'll end up with a lot of work pulling excess shoots every spring unless you begin to do some sever pruning prior to this point. i'm not making things up, just trying to let you all in on what is to come.