Photoperiod

Photoperiod refers to cannabis plants that rely on changes in light duration to trigger flowering. These plants typically require a shift to shorter days (longer nights) to initiate reproductive growth, commonly 12 hours of light and 12 hours of darkness. Photoperiod genetics dominate both historic landrace and modern breeding programs, as they allow breeders precise control over crop timing through environmental manipulation. Indoor cultivation of photoperiod strains requires deliberate light scheduling, while outdoor grows align with natural seasonal transitions. This classification contrasts with autoflowering varieties, which flower based on age rather than light cycles. Understanding photoperiod mechanics is foundational to cannabis breeding, cultivation timing, and strain stability work.

Breeders maintain photoperiod lines to preserve genetic diversity and enable extended vegetative growth periods for phenotype selection, clone production, and crosses. Photoperiod stability—the consistency with which plants respond to light cues—is a key quality marker in breeding programs.