PROBLEM TO BE SOLVED: To obtain a lightweight planting block which has excellent water holding property, water permeability and durability, with which a plant can be raised without using soil and which is suitable for forming a three- dimensional flower bed on the rooftop of a building, a veranda, etc. SOLUTION: This planting block for three-dimensional flower bed is equipped with a plurality of planting boards 1 porous ceramic obtained by firing and forming expandable slag granule made by adding a blowing agent to slag, a supporting block 2 having supporting surfaces of the boards, made into curved surfaces or sloping surfaces fit for flower bed formation. The supporting surfaces are equipped with projecting stripes for preventing displacement of each board between the boards. The contact face of each board of the supporting block is provided with a channel 4 for watering piping and water from watering piping 5 is supplied through the planting board 1 to plants.
