In Harper Lee's To Kill a Mockingbird, what is the collard patch?

In Chapter 6, Jem plans a night-time raid on the Radley house hoping to see Boo through a window. In order to get close to the house, the children have to travel through Nathan Radley's garden. Jem warns Scout and Dill not to walk in the collard patch because "they will wake the dead." (Lee 71) A collard is a vegetable. Specifically, it is a type of kale that is grown in the South. Collards are short plants with huge green leaves, and the children try their best to avoid walking through them. The children quietly walk through his garden and Jem manages to see a shadow in Radley's window. Jem gets spooked when the shadow stops about a foot beyond him, and he jumps off the porch toward Scout and Dill. Scout trips and falls as the children run through the collard patch. Nathan Radley emerges from the house and fires a warning shot into the air. The children narrowly escape, and Jem loses his pants after they get caught in Nathan's fence. Later on, when the neighbors are discussing what happened outside Radley's house, Stephanie tells Jem that Nathan scared a Negro in his collard patch. Nathan does not suspect the children, and thinks that a black man was walking through his collard patch.