I'm in MN USA, it's not in a ditch but there is one about 6 feet away. It came up looking like grass, at first I thought it was Pampas but I don't think it will survive MN winters and I never saw Pampas with flowers. I have no idea if it's native or not.
Here it is a few weeks ago, circled.

The ditch, if you want to call it that, is just the other side of the cedars in the pic.