Plant growth substrates that lack organic components, such as organic soil, peat or bark material. In certain aspects sponge-like matrix materials are provided that are porous, retains water and can be used to maintain plant growth. Matrix materials, for instance, can comprise an admixture of a hydrophilic polymer, such as a polyurethane, and an amorphous silica. Methods of growing and maintaining plants and plant parts in such materials are also provided.
