I have a monti that is like a vase now. They are easy to frag, just grab a piece and snap it off. Careful you don't snap off more than you intended to though -- they are pretty easy to snap.
I have one that a year and a half ago was the size of a thumbnail and it's about the size of a mini basketball now so frag it how you would like it to grow and shape out if you can/want to.