To effectively use the ground by planting to a point close to the boundary line.

The boundary block 1 is composed of a surface part 2 and back part 3 having extended rectangular plate forms and a connection part 4 integrally connected with the surface part 2 and the back part 3. The connection part has vertical recesses 4a formed on the right and left end faces and has through-holes 4b penetrating the part in lateral direction. Soil 33 for planting can be filled in a space between the surface part 2 and the back part 3 of each boundary block 1 in the case of placing the boundary blocks 1 along the boundary line.