William Black, writing for The Atlantic:
Southern whites saw their slaves’ enjoyment of watermelon as a sign of their own supposed benevolence. Slaves were usually careful to enjoy watermelon according to the code of behavior established by whites. When an Alabama overseer cut open watermelons for the slaves under his watch, he expected the children to run to get their slice. One boy, Henry Barnes, refused to run, and once he did get his piece he would run off to the slave quarters to eat out of the white people’s sight. His mother would then whip him, he remembered, “fo’ being so stubborn.” The whites wanted Barnes to play the part of the watermelon-craving, juice-dribbling pickaninny. His refusal undermined the tenuous relationship between master and slave.
Emancipation, of course, destroyed that relationship. Black people grew, ate, and sold watermelons during slavery, but now when they did so it was a threat to the racial order. To whites, it seemed now as if blacks were flaunting their newfound freedom, living off their own land, selling watermelons in the market, and—worst of all—enjoying watermelon together in the public square. One white family in Houston was devastated when their nanny Clara left their household shortly after her emancipation in 1865. Henry Evans, a young white boy to whom Clara had likely been a second mother, cried for days after she left. But when he bumped into her on the street one day, he rejected her attempt to make peace. When Clara offered him some watermelon, Henry told her that “he would not eat what free negroes ate.