Question
I live in Pennsylvania and have one GORGEOUS scotch broom!!  It has grown quite a bit over the last few years and I would like to prune it but I'm not sure of the correct way to do it. My understanding is that they are hard to kill, but I think I could do that without trying!  I don't want to lose it and could use your expertise!

Answer
Yes by all means prune away. Cut as much as you would like. Best time is right after they finish blooming.
If your broom shows up with dead spots here and there, it is not your fault. They do that. Just cut the dead off and they will be as good as new again. They are very hard to kill.