I have just removed grass stains from my son's jeans! After a regular wash I noticed they were still there and bright. I poured hot water on the stain and some "oxy clean" , scrub and let it sit (I didn't let sit too long, I had to get the wash started). Maybe repeat the process and scrub, let sit overnight. I have just checked the pants and the stains are mostly removed with very little fain spot. I am going to put the pants out in the sun and I'll be they'll be gone.