A device for preventing plant growth around a post, comprising an opaque sheet, an opening in the sheet, and a slit extending entirely from the opening to the perimetric edge. A fastener structure is arranged to fasten one of the edge portions to an other of the edge portions in a relationship wherein the edge portions overlap thereby effecting a slope of the sheet downwardly from the opening to the perimetric edge and wherein the opening is shaped to have a first shape when the edge portions are not overlapping and to have a second shape to conform to the post when the edge portions are fastened in the overlapping relationship.
