A method for making a growing medium includes a step of combining tree bark and/or wood components together to form an initial composition; heating the initial composition to a temperature greater than about 149° C. under steam in a pressurized vessel; processing the initial composition through a refiner with a plurality of opposing disks to obtain the fibrous growing medium, the refiner separating fibers from each other; wherein the growing medium has total porosity of 88 volume % or more.