An illumination device for plants includes a lighting unit mounted on a lamp seat and including a cold cathode fluorescent lamp and a light emitting diode (LED) unit. A driving unit is mounted to the lamp seat, is coupled to the cold cathode fluorescent lamp and the LED unit, and is operable so as to drive the cold cathode fluorescent lamp and the LED unit such that the cold cathode fluorescent lamp and the LED emit respectively color lights having respective wavelengths. A dimming unit is coupled to the driving unit, and is operable so as to output a dimming output to the driving unit. The driving unit drives the cold cathode fluorescent lamp and the LED unit based on the dimming output from the dimming unit so that the color light emitted by each of the cold cathode fluorescent lamp and the LED unit has a respective light intensity.