Thermoformed double tray system for cultivation of plants including a top tray which is stacked with a bottom tray. The top tray has cells for receiving a substrate. The bottom tray provides rigidity to the double tray system. The bottom tray has a baseplate which is provided with support elements to support the top tray. The baseplate has an outer edge which defines the outer contour of the bottom tray. A groove shaped deepening in the baseplate is extending in parallel with the outer edge. The deepening increases a bending stiffness of the bottom tray and provides rigidity to the double tray system. The deepening is provided with a reinforcing ribs which cross the deepening.
