Short Day Phenotypes

Short day phenotypes refer to cannabis plants that initiate flowering based on photoperiod thresholds, typically triggering bloom when daily light exposure drops to 12 hours or less. These plants evolved in regions with distinct seasonal light cycles and remain photoperiod-dependent, requiring specific light/dark ratios to transition from vegetative to reproductive growth. Short day phenotypes contrast with autoflowering varieties, which flower based on age rather than light duration. Breeders maintain photoperiod-dependent lines for research, preservation of landrace genetics, and breeding programs where flowering timing must be controlled. Understanding short day behavior remains foundational to cannabis cultivation and genetics documentation, particularly in regions with natural seasonal variation.

Breeders working with short day phenotypes maintain precise photoperiod controls to stabilize flowering times, test genotype stability, and develop crosses with predictable light-responsive traits. Short day genetics serve as parent material for hybrid breeding programs and are essential for preserving heirloom cultivar lineages.