Photosensitivity

Photosensitivity in cannabis refers to a plant's responsiveness to light cycles, particularly the photoperiod (ratio of light to darkness) required to trigger flowering. Traditional photoperiodic cultivars require a shift to shorter days (typically 12 hours or less of light) to initiate the transition from vegetative to reproductive growth. This trait is controlled by phytochrome and other light-sensing proteins that regulate developmental timing. Non-photoperiodic varieties, often called autoflowering types, flower based on age rather than light duration. Understanding photosensitivity is fundamental to breeding schedules, cultivation planning, and selecting appropriate genetics for different growing environments and seasons.

Breeders manipulate photosensitivity to create cultivars suited to specific climates and production systems. Combining photoperiodic and autoflowering genetics allows development of hybrids with flexible flowering triggers, while selections for extreme day-length sensitivity enable targeted outdoor or controlled-environment cultivation strategies.