The present invention relates to an inflatable air bag for closing off passages when storing plants in boxes for the purpose of ventilating the plants in the boxes during (prolonged) box storage, in which the air bag is configured to close off a passage between two rows of stacked boxes in a vertical direction at least substantially against air displacement, in which the air bag is provided with an air supply connection for supplying a gaseous medium for inflating the air bag during use. According to a first aspect of the present invention, the air bag is characterized by the fact that the air bag is configured to, in use, increase in length between the rows of stacked boxes from the ground in a vertical direction and in which the air bag is furthermore provided with a forcing member which is attached on the inside of the air bag to the first free end and is configured to cause the air bag to roll up inwards when the air pressure in the air bag decreases.
