Disclosed is a substrate for out-of-ground cultivation by using a substrate consisting of mineral fibers. The substrate according to the invention is of limited dimensions and is used for the cultivation phase corresponding to the development of seedlings. This substrate, being of generally parallelepipedic shape, exhibits on its lower face added feet or pedestals that project therefrom and isolate the substrate from the ground on which its rests. The substrate according to the invention makes it possible to improve cultivation conditions.