Photoperiod

Photoperiodic flowering is the natural reproductive trigger for both Cannabis indica and Cannabis sativa, evolved as an adaptation to seasonal day-length changes at temperate and equatorial latitudes. The plant detects shortening days through the phytochrome system — a light-sensitive protein that registers extended dark periods and signals the transition from vegetative growth to reproductive (flowering) growth. Indoor growers exploit this by maintaining 18/6 or 20/4 light schedules during the vegetative stage to keep plants growing leaves and branches indefinitely, then flipping to a strict 12/12 cycle to induce flowering. Outdoor photoperiod plants flower naturally in late summer/early fall as days shorten, harvested between September and November in the Northern Hemisphere. Critical considerations: any light leak above 1-2 lux during the dark period (a phone screen, a streetlight, an indicator LED) can stress the plant into reverting to vegetative growth or triggering hermaphroditism. Photoperiods reward patience and skill — they yield 2-4x more per plant than autoflowers, can be cloned indefinitely from cuttings, respond well to high-stress training (topping, scrog, supercropping), and reach the highest THC potencies in the industry. The total seed-to-harvest cycle runs 14-20 weeks: 4-8 weeks vegetative + 8-12 weeks flowering.