Growth device for crop and a cassette (22) for such a growth device, the growth device comprising a panel-shaped structure (1), a substrate (2) included in the panel-shaped structure (1) for receiving crop (3), at least one water reservoir (4) included in the panel-shaped structure (1), connecting means (6) to bring the water reservoir in communication with the substrate (2) for moistening the substrate (2), wherein the water reservoir (4) extends substantially above a bottom side (B) of the substrate (2) in a vertical position of use of the growth device.