A plant cultivation method for increasing the phytochemical content of a Labiatae plant is provided. The plant cultivation method includes cultivating the Labiatae plant in a visible light environment having a dark period and a light period during which the Labiatae plant is exposed to visible light in an alternate manner, and performing treatment with UVB radiation during the light period for at least one day before harvesting. A cumulative dose of the UVB radiation may range from 0.54J/m2 to 4.32 kJ/m2.