A serrated bread knife (not your best one!) cut as close to the ground as possible in early spring works well. Because of the way grass grows eventually you end up with dead centers.

You can dig up the clump and separate the living out side portion to replant and throw away the dead centers. Its not a fun job but it works.

I cut my ornamental grass "Standing Ovation" down to the base before it begins to sprout. Once certain perennials begin to die in the center (yet clearly grow along the edges), it's time to divide them.

Im starting to think its a type of bamboo. Oh no isnt bamboo very invasive? its near my neighbors peoperty line too. it came from a flower arrangement i gave my wife years ago

That’s what ornamental grass does, unfortunately - it dies out in the middle. A sawzall is the tool of choice.

Turns out what i had was pampus grass. it had these beautiful plumes starting in august and would last all winter til i cut back in fall