A product holder assembly for a mobile cultivation of plants along a path in a hall includes a product holder having a bottom and an upstanding circumferential wall extending from the bottom, a first space extending from the bottom of the product holder along the wall to allow a medium or substrate for roots of the plants to receive nutriments and/or support from, a grid system arranged to be placed on the product holder to cover the first space in the product holder and to separate the first space from a second space adjacent to the grid system at a side of the grid system facing away from the first space, wherein the grid system is arranged for holding a plurality of separate plants, the roots of which to reach for the first space and the leaves of which to reach for the second space, wherein the grid system is arranged to operate in conjunction with an air duct system.