The hedge trimmer will have a max diameter cutting ability. As long as the diameter of the weeds does not exceed the specifications, a hedge trimmer will cut tall weed stems. Grass blades, I do not know.

Jim, the more I think about it, using a hedge trimmer wouldn't work. I am going to try to put something over them to cover them like metal siding which I have plenty here.

You can also put some cardboard down...I've done on the grapes.