I think it's asked a bit too much for grass, actually, the restriction to non-commercial. Grass is usually just a tiny part of an artwork, hardly visible among other grasses, flowers, rocks and whatnot. Same as in reproduction rights for paintings. I have one of my paintings on a wall. I can ask reproduction rights if the wall+painting is being photographed, and published (commercially) only if it is a bigger, essential part of that photo, or the essence of that photo, not if it happens to be there.
I can imagine though, if you render his grass as main subject, there's the restriction.
Just use other grass...