LifeCycle Events: Death, Burial, and Bereavement: Putting Grass or Earth on a Tombstone:
Why do we put grass or earth on a tombstone?
The source seems to be the B'er Hetev on Orach Chayim 224:8, quoting Derashos
MaHaRaSh: We pull up grass or a clod of earth and put it on the monument
in honor of the dead in order to show that someone has visited the grave.
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