Abstract: The production of a fertilizer from tree bark is improved by a process of the type wherein crushed waste bark is treated together with waste molasses under elevated pressure and at a temperature of 75.degree. to 140.degree. C. for a time of 10 min. to 2 hrs. said time being dependent on the treatment temperature, and wherein the improvement comprises adding of yeast to the waste molasses, and maintaining its temperature at 30.degree. to 40.degree. C. for 35 to 45 hours, whereby its pH value decreases to 3-4, before it is mixed with the ground waste bark.