grass tile

Hi there, can anyone help with this? : ( I've been trying to plant fruit trees around my farm, and I also used the CJB Item Spawner, then after a few days this appeared at the bottom of my farm. If you look closely you can see a dirt tile overlapping with the border grass tile. I've since then...

I would like to be able to craft or buy floor tiles that look like regular short grass and would change with seasons just the same way. It would be so nice to cover empty ground with grass instead of paving it with stone or wood tiles. The farm should look green. I know there are mods for that...