A fence post top cap for retaining a wire trellis thereon consisting of a sheet metal body (20) configured to fit snugly on the top of a metallic studded fence post. The body includes a front (22), sides (24), a top (26) and a bottom (28) with the sides extending at obtuse angles from the front and having a plurality of bores (40). The top has a bent right angle horizontal lip (42) that extends rearward from the front, with the sides remaining upright forming a U-shape for resting trellis wires on the lip while containing them between the upright sides. The bottom, including the front and sides, conform to fence post exterior dimensions and fit tightly onto the posts concave face (32) with the studs (36) engaging the top cap front. A first cotter pin (44) penetrates the bores (40) in the sides between the posts studs holding the top cap in place vertically and a second cotter pin (46) disposed through similar bores retain trellis wires (48) that are strung between the posts to form a trellis.