Albert Barnes Commentary 2 Kings 9:21

"And Joram said, Make ready. And they made ready his chariot. And Joram king of Israel and Ahaziah king of Judah went out, each in his chariot, and they went out to meet Jehu, and found him in the portion of Naboth the Jezreelite." — 2 Kings 9:21 (ASV)

Make ready - This literally means, (as noted in the margin) “Blind,” that is, “Harness the horses to the chariot.” The king had no suspicion of Jehu’s treason. He probably imagined that Jehu was bringing him important news from the war. Ahaziah’s decision to accompany him is significant of the close friendship that united the uncle and the nephew. They went out not “against” Jehu, but rather “to meet him.”

In the portion of Naboth - This is no longer called a “vineyard” (1 Kings 21:1–18); it was probably thrown into the palace garden and used for the purpose Ahab originally wanted. The approach to the city on this side must have passed either through it or close by it.