Under the 'Density Texture' option of the grass select image and use a black and white map, white where grass grows and black where it doesn't.
Have 3 materials (and slabs) Full Grass, 25%-60%, Full Tile.
It shouldn't be impossible.
This might be of use to you.
https://www.facebook.com/geometra.pesce.patrick/videos/1339738926083208/
Versions 10 to 27
Metabox Prime-X P775DM2-G (Clevo),
GTX 1060 6GB GDDR5 VRAM - G-Sync,
i7-6700K (8M Cache up to 4.2 GHz),
32GB DDR4 2133MHZ,
512GB SATA 3 M.2 SSD,
Win 11 64