A plant substrate consisting of (a) 25 to 100% by weight of an open-celled melamine/formaldehyde foam, (b) 0 to 75% by weight of other synthetic plant substrates and/or mineral soil and (c) 0 to 25% by weight of one or more systems for releasing active substances and/or of other additives, can be stored and transported in the absence of any water and makes possible a good aeration in the soil.