To realize a root-preventing sheet with outstanding shape maintaining properties while being thin and light that even when affixed has no wrinkles, is difficult to tear, has excellent applicability, durability and adhesiveness and demonstrates definite root-preventing effects at low cost. The above problem is resolved by realizing a root-preventing layer structure set up on the construction surface of the soil layer that the plant is planted in and which prevents extrusion into the outer part of the soil layer of the plant root comprising: a resin film having the strength to be able to prevent extrusion of the plant root affixed to the construction surface; and an adhesive layer formed on the back face of the resin film, wherein a cover tape, which has an adhesive layer on the back face and has enough strength to be able to prevent extrusion of the plant root, is affixed to mutually abutting or overlapping resin film parts of the root-preventing layer to prevent extrusion of the plant root, and the thickness of the adhesive layer of the cover tape is formed to be smaller than the diameter of the extruding tip of the plant root.