Charles Ellicott Commentary 1 Kings 21:13

"And the two men, the base fellows, came in and sat before him: and the base fellows bare witness against him, even against Naboth, in the presence of the people, saying, Naboth did curse God and the king. Then they carried him forth out of the city, and stoned him to death with stones." — 1 Kings 21:13 (ASV)

Carried him out —as usual, in order to avoid polluting the city with blood—possibly to his own ground, the coveted vineyard itself.