PROBLEM TO BE SOLVED: To provide a supply method of watering and a controller of watering which control timing of watering and a watering amount for higher production in plant cultivation.SOLUTION: In a supply control method of watering in plant cultivation, above-ground part environment is detected by measuring the temperature and the humidity of an above-ground part intermittently or continuously, and furthermore underground part environment is detected by measuring a moisture content in soil intermittently or continuously, and timing of watering and a watering amount are controlled based on the detected above-ground part environment and underground part environment.