The present invention relates to a method for processing grass or hay as paper pulp having the steps of pre-reducing the grass or hay with a bale breaker and/or a shredder to an average fiber length between 500 mm and 10 mm, preferably between 120 mm and 10 mm, removing impurities and foreign or extraneous substances by means of a cyclone; reducing and fibrillating the grass or hay in a fiber mill, fraying the grass or hay; and screening and/or sifting the grass or hay by means of a circulating-air separator and/or a cyclone screener.