Abstract: A plant cultivation and support structure in the form of a strongly hygroscopic block having a flat base, an indentation located in the top large enough to hold a seed or a seed pellet, an open bore leading from the bottom of the indentation to the base, and at least one transverse channel extending clear through the block at the base. A plurality of blocks may be formed in rows and columns of an integral plate subdivided by mutually perpendicular sets of spaced narrow congruent grooves in the top and bottom surfaces of the plate. The material of the plate is a foamed light, brittle plastic having an elongated tandem cell structure with porous walls, a pH value not exceeding 5.2, and specific gravity between 3 and 15 kg/m.sup.3.