This invention includes a coherent growth substrate product formed of mineral wool, the product having two opposed top and bottom surfaces and a channel which is open at the bottom surface and extends from the bottom surface at least 50% of the height of the growth substrate product and wherein the volume of the growth substrate product is not more than 150 cm3.本発明は、ミネラルウールで形成される密集した育苗培地製品(1)であって、対向する2つの面すなわち上面(4)および底面(5)と、底面(5)で開口し、底面(5)から育苗培地製品(1)の高さの少なくとも50%延在するチャネル(2)と、を有し、育苗培地製品(1)の体積が150cm3以下である、製品を含む。