Abstract: A low density (5-12 Kgs/M.sup.3), rigid, unicellular (i.e. closed cell) expanded polyurethane foam is perforated through at least part of its thickness by mechanical means, resulting in a hydrophilic, heterocellular (open cell) foam, whereby to facilitate the passage of emergent plant roots and also to provide groups of enlarged voids (in contrast to the fine cell structure of the unmodified foam) so as to facilitate water absorption and retention.

Abstract: A synthetic substrate for use in the rooting of cuttings and the raising of seedlings, comprising an expanded, semi-rigid, substantially hetero-cellular plastics material having a plurality of regions of relatively low density for receiving cuttings or seedlings to be propagated. The regions of low density are separated by regions of relatively high density which exhibit higher capillarity than the lower density regions.One way of forming the aforegoing substrate is to subject predetermined regions of a block of foamed polyurethane or other suitable, relatively low density plastics material to heat and pressure whereby to selectively compress and permanently deform the low density foamed material to produce the regions of relatively high density.The synthetic substrate of the invention may also be in the form of capillary matting for use in supplying water and/or nutrients to plants.