Just noticed that this thread was created a couple of months ago, whoops. But here I tried an edit for you -
The second style of grass down was your best I think, they most suited the style of the rocks. No harsh dark lines running through them. I used that as a jumping off point. Rather than trying to render the individual blades of grass, which can get very noisy at this size, I thought about how long grass sometimes clumps together in a pleasing way. I also added a shadow cast by the grass on the rocks.
Then I did a little AA and stuff on the rocks to smoothen them out a bit, like I changed the large rock at the bottom so that it doesn't look like it's being lit from below anymore. Hope it helps if you see it!