Substrate compression process and product

A compressed horticultural slab comprising:

• a fibrous substrate comprising a plurality of compressed fibers, the substrate having a moisture content of up to about 20 to 25 wt. % and having a final loose bulk density defined by a formula (I):
• ρx=ρ1*x, (I)
• where:
• ρx is the final loose bulk density,
• ρ1 is the initial loose bulk density, and
• x is the compression factor including any number between 4 and 60,
• wherein the compressed slab has a substantially rectangular shape and uniform dimensions throughout its length and a higher volume of capillary pores than non-capillary pores.

A method of forming a compressed horticultural slab, the method comprising:

• filling a container with a fiber substrate having a plurality of loose metered wood fibers having initial loose bulk density ρ1;
• pressing the fibers in the container for a dwell time under such pressure that a compression ratio of the initial to compressed fiber of 1:4 to 1:60 and final loose bulk density ρx is achieved, wherein ρx>ρ1, while the fibers obtain the shape and at least some dimensions of the container such that the slab is formed;
• and
• removing the slab from the container.