Short Day Photoperiod

Short day photoperiod refers to cannabis plants that initiate flowering when daily light exposure falls below a critical threshold—typically around 12 hours or less. These plants are photoperiod-dependent, meaning their reproductive cycle is directly regulated by light duration rather than age alone. Most traditional landrace and heirloom cannabis strains exhibit short day photoperiod behavior, having evolved in equatorial and subtropical regions where seasonal light changes trigger flowering. Understanding photoperiod classification is foundational to breeding programs, as it determines growing windows, indoor cultivation requirements, and geographic suitability. This trait contrasts with autoflowering genetics, which flower independently of light cycles due to Cannabis ruderalis genetics.

Breeders working with short day photoperiod genetics must manage light schedules carefully in controlled environments, typically switching to 12/12 hour cycles to induce flowering. This classification is essential for preserving traditional strain genetics and creating photoperiod-stable F1 hybrids suited to specific climates and cultivation methods.