A method and device (1) for producing a stabilized growing medium for cultivation of a plant (3) or seedling. The method comprises the steps of providing a receiving unit (11) for containing the rooting plug to be formed and placing a root structure (5) of a plant (3) or seedling in the receiving unit (11). Further, the method includes the steps of filling the receiving unit (11) with slurry material forming a stabilized growing medium and curing the slurry material in the receiving unit (11) while holding the root structure (5) of the plant (3) or seedling in the receiving unit (11).
