A device for the tensioning of wires supporting the vegetation of plants that includes at least one wire tensioning member, one support member adapted to support the tensioning member in rotation, and a blocking means to block the rotation of said tensioning member. The tensioning member includes a metal fork bent and the support member has at least one through-hole penetrated by the tensioning member so that said tensioning member rotates with respect to the support member. The means for blocking the rotation of the tensioning member include at least one recess or groove that reversibly engages with the tensioning member.