Photoperiod refers to the daily duration of light exposure a plant receives. Many plants use photoperiod as a signal to trigger flowering, dormancy, or vegetative growth. Indoor growers control photoperiod by setting timers on grow lights to manipulate plant behaviour regardless of the season.
Key Facts
- Long-day plants flower when light exceeds a critical threshold (typically 14β16 h)
- Short-day plants flower when darkness exceeds a critical threshold (typically 12+ h of dark)
- Day-neutral plants flower regardless of photoperiod (e.g. cucumbers, tomatoes)
- Indoor growers use 18/6 (light/dark) for vegetative growth and 12/12 for flowering
- Even brief light interruptions during the dark period can delay or prevent flowering
- LEDs and timers give indoor growers precise, season-independent control