PURPOSE: To allow the growth of a plant by mixing a vegetation material formed of a water absorptive polymer, seed and sand into the void part of a base plate formed with porous concrete to form a vegetation board.

CONSTITUTION: A vegetation board 3 is formed of a base plate 5 formed with porous concrete, and a vegetation material 6 formed with a water absorptive polymer, seed and sand in its void part 5a. The water absorptive polymer is formed by dissolving an acrylic copolymer as a dispersing agent into a fatty hydrocarbon, dispersing an acrylic acid and an aqueous solution of alkali metal salt thereto, conducting suspension polymerization in reverse phase, and further cross-linking the resulting solution with a cross-linking agent in the presence of an inorganic material followed by drying. An exterior material covered with rich green thus can be obtained without planting work.