Shade Gardening: Suggestions for deep shade under cedar and fir trees, 1 by Jamesk

Jamesk wrote:
I've got a problem area along the east side of my house. Almost nothing wants to grow there under two giant trees. The right trunk in the photo is a 80' cedar, the left trunk is a 100' Douglas fir.

I've tried and tried to get shade tolerant plants to grow in this area, but so far, not much luck with anything except Oxalis oreganum.....and even that doesn't really want to thrive. Even Pachysandra doesn't want to go. I've amended and amended with compost, nothing seems to help. The problem doesn't seem so much to be the deep shade, but rather, that the two trees suck up every drop of moisture, no matter how much water I pour on.

Any suggestions for something that will fill in the area? Both trees dump tons of trash all winter long, so anything growing there has to tolerate being practically buried over the winter, and love dry-as-a-bone deep shade. It's a part of the garden that no one but me usually sees, so stunning beauty isn't necessarily a requirement. I just don't want it to have the neglected look that it has now. I'm in Seattle, zone 8b. Any suggestions gratefully accepted.