A modular plant growing device (100) includes a main frame (1) mounted on an upright supporting surface (200). The main frame (1) is configured with an accommodating space (15) defined by an upright rear plate (11), an inclined top plate (12) extending gradually and upwardly from an upper end (111) of the rear plate (11), an inclined bottom plate (13) extending gradually and upwardly from a lower end (112) of the rear plate (11), and opposite lateral plates (14) for receiving a plant unit. The top plate (11) is formed with an inlet unit permitting flow of liquid for plant growth into the accommodating space (15) therethrough. The bottom plate (13) is formed with an outlet unit disposed adjacent to the lower end (112) of the rear plate (11) and permitting leakage of the liquid from the accommodating space (15) therethrough.
