Perhaps soaking in napisan might help, but I’m not sure if it would fade the jeans.

Bi-carb and vinegar will lift most stains.

Mix bicarbonate and vinegar. Leave for an hour. Scrub then with sard wonder soap. This removes all stains I have ever had.

I second the napisan paste method. I use it on my cricket whites, and comes out clean after 2-3 cycles.

I give it a good going over with sard wonder soap, then make a paste of napisan (using cold water). Then in the machine with another capful of napisan on a cold wash, then dry in the sun. Works for most stains I find. Also get onto them ASAP. I find the longer I leave it, the harder the stains are to get out.

Good old fashioned sard wonder soap. I use it on everything. Wet the stain rub on soap and leave for a day then was everything comes out but not the colour!

AMWAY LOC, before laundering apply the LOC liquid neat to the stain and leave on over night, the next day launder as normal.
Nifty all purpose surface cleaner is also excellent for removing stubborn stains, better than pre-wash stain removers.

Napisan (in the pink container) make a paste, leave on stain for a few hours, give it a bit of a rub, if really bad, soak overnight, (I always use cold water as if some of the grasses have sap in them hot water can set the stain) wash in cold water with good detergent and some napisan, this should get the stain out, I never have any problems with cricket whites and they have different types of grass stains and mud stains, but make sure you only use cold water as this allows you another chance, once you have used hot water then the stain is usually set and there is not a lot you can do.

I would suggest a paste of Napisan and rub it into the stains and then soak overnight. Good Luck!

Spray with Orange Power Pre-Wash Stain Remover, rub it and soak in water overnight. Wash in your washing machine. I usually use liquid Detergent. Depending on how many times you have already tried to remove the stains in your washing, it may not come off. I find I get a lot of stains off with Orange Power that won’t come off with other pre-wash stain removers.

strangely, this comes down to the colour of the jeans.

A basic answer would be to soak in Nappy San in HOT water for half and hour and the wash in warm wash. cold rinse

This will sound so silly, but add a can of coke to the wash….