First, I went at the area with the rototiller, but soon I discovered that the planting area is also where one of the underground sprinkler hoses is installed, so I couldn't keep using the machine without the danger of severing the sprinkler line. So it was time to sit down on the ground with a hand trowel and start digging it up by hand. I worked all day, and finally quit when I was too tired to go on - there's still a few feet left to go. The roots were so mashed together, I had to stab them with the trowel to try to sever them in order to pull a bit out. One of them (I think it's the Ribbon Grass) has a long underground root system with joints, kind of like a foxtail weed, and out of each joint, a new sprig of grass can grow. Everywhere I looked, I could see these pinkish fangs of grass poking out, ready to leap into action. Good thing I started now, until they'd been able to sink more roots down. In the midst of all this tangle of grass, a delphinium had managed to take hold, against all odds, so I had to try to remove the roots without disturbing it. It must be pretty hardy to have held out against all this bossy competition, so I think it will be OK.
I'd have liked to keep a little of the Miscanthus, it's so pretty, but logically I realize that I'd just end up doing this all over again in a few years' time. I know just pulling them out won't be enough, either; the way these plants work, if you leave a little scrap of root in the ground, it will regenerate and put up another plant, so I'll probably be hunting these things down for a long time. Once summer comes, if things are desperate, I can give them a good blast of RoundUp and kill them that way, but I prefer to avoid the chemicals if possible.