What family ritual does granddaddy teach the girls while they are staying with him in Lansing in the novel, What the Fireflies Knew?

The greens that Granddaddy teaches KB and Nia how to prepare are symbolic of their ties to their relatives that came before them. Granddaddy teaches them to wash the greens just as he was taught by his elders. They prepare these before the family party for the Fourth of July that occurs the next day.