Can anyone tell me the actual meaning or reason for the white string attaching graves at Wats?

I understand the white string in ceremonies but can't find any information on the graves.

Thanks

It would be the same probably. Someone has probably held some sort of merit making ritual and the string is for sending or collecting 'merit' vibes.

It's likely that the white string is tied around the graves as a mystical measure to prevent "bad" ghosts from escaping from their graves to harm the dead and the alive and to protect "good" ghosts from bad spirits.

Certain Buddhist practices in Thailand are obviously occultism.