The present invention relates to a method of producing a coherent growth substrate product formed of man-made vitreous fibres (MMVF), comprising the steps of (i) providing MMVF； (ii) providing an uncured binder composition； (iii) providing an additive； (iv) forming a mixture of the MMVF, the uncured binder composition and the additive； (v) curing the uncured binder composition in the mixture to form the coherent growth substrate product； wherein the uncured binder composition comprises at least one hydrocolloid； and wherein the additive is a micro-organism, fungus, biologically-active additive or combination thereof.
