A modular field planting system adapted for installation on a roof surface includes an arrangement of substantially identical tray members with each tray member containing two tray compartments. An array of first tray members is positioned on the roof surface with the tray members being in contiguous relationship and oriented in a first direction. A second tray member positionable in overlying relationship with respect to the first tray and rotated 90.degree. with respect to the first direction, is nestably seated within corresponding tray compartments in each of two adjacent first tray members. A wicking material in the first tray member is placed in communication with a wicking material in the second tray member when the respective first and second tray members are seated. The first tray member is adapted to provide a reservoir for water and the second tray member is adapted to retain a growth medium whereby the wicking material provides continuous moisture migration for hydrating the growth medium.