Short Day Induction

Short Day Induction (SDI) refers to the photoperiodic mechanism cannabis plants use to transition from vegetative growth to flowering when day length drops below a critical threshold—typically around 12–13 hours. This trait is fundamental to traditional photoperiodic cannabis genetics, especially in landrace and outdoor-adapted cultivars that evolved under seasonal light cycles. Breeders working with SDI genetics select for reliable flowering initiation and predictable bloom timing, making these lines valuable for regional cultivation and breeding programs targeting specific latitude responses. SDI is distinct from autoflowering genetics, which flower independently of day length through different genetic pathways. Understanding SDI mechanics helps breeders develop cultivars suited to particular growing environments and seasons.

Breeders prioritize SDI stability when creating regionally adapted cultivars and outdoor photoperiodic lines. Selection for consistent short-day response and flowering window precision improves predictability in breeding programs and seed production.