Hi,
One area in my backyard, the flower bed, is in a sad shape. Don't know what happened; somehow the soil has changed: there's lots of moss, and some kind of pesky weed with yellow flowers, that acts like a ground cover, is taking over. I still have a cup plant there, and four peonies, that are hanging in, although barely; peonies especially don't look so good. I had to get rid of everything else, and would like to plant something in the bare spots.
I've always wanted to have decorative tall grasses in my garden. Which in your experience could do well in these conditions: partial sun, mossy soil?

https://extension.umd.edu/reso...

Good list, pay attention to details like (Northern sea oats can self sow agressively- yes it does)

You might need the part shade ones (chart at the bottom). Moss suggests shade and or poor drainage. Maybe this is why the peonies aren't happy? But peonies just don't look happy in October here anyway.