Abstract: A plant growing frame for securing a number of form-stable growing medium blocks so that, after they are placed in the frame, they are mutually separated by air spaces running from under the bottom and up between and over the growing medium blocks to control root growth out of the blocks by root air pruning and thereby prevent root growth from one block to another. The frame includes a planar network of criss-crossing horizontally extending spaced double rib members defining a plurality of vertically extending open ended block-receiving openings for receiving the blocks therein and a plurality of air-passage forming openings. The space between the double rib members defines the block-receiving openings and the space between each rib of the double rib members defines the air passage forming openings. The air passage forming openings encircle each block receiving opening and separate each block receiving opening from all neighboring block receiving openings.