It is possible to plant fruit trees on grass tiles, however on the dark green grass if the tile has a "tuft" of grass texture on it like so... You won't be able to plant a fruit tree on that spot. Regular trees are fine, but not fruit trees. Interesting as well, you can plant fruit trees on the "tuft" textures on the light green grass- its just the dark green irregularities that are forbidden. Does anyone know of a mod that circumvents this?