PROBLEM TO BE SOLVED: To provide a coherent growth substrate enabling optimum growth/ generation and suitable for a grow-block, a grow-slab, etc., by being based on a synthetic matrix containing clay in a specific quantity to make a moisture content of prescribed water absorptivity lower than a prescribed value. SOLUTION: The desired coherent growth substrate is based on the synthetic matrix consisting of mineral fiber plastic, foaming clay and the mixture of them containing the clay (particle sizes are preferably 100μm to 10 mm) by 0.1 to 25 wt.%, preferably 1 to 20% and more preferably 2 to 10%, so as to make a moisture content lower than 15% by volume at a absorption pressure of pF=2, and is 30-200 kg/m<3> of a density preferably.
