A modular green roof and/or green wall system includes a plurality of trays adapted to support vegetation and soil therein. The trays are sized such that a person may easily lift them and install them in a pre-vegetated state upon a roof or a wall. The trays are further designed to enable subterranean irrigation lines to be inserted therethrough, thereby hiding the irrigation lines from view. Biodegradable walls may be added of different heights to the trays to support different types of vegetation, as well as to create terracing for a given installation, if desired. A wicking material may be inserted into the tray and positioned such that is makes contact with wicking material in adjacent trays, thereby spreading moisture between trays through the capillary action of the wicking material.