Flowering Response of Cannabis sativa L. ‘Suver Haze’ under Varying Daylength-Extension Light Intensities and Durations

Abstract

Daylength-extension lighting (DE) is used in the cannabis industry to increase plant size and produce cuttings by regulating flowering and extending the vegetative stage. Growers have reported incomplete or transitional inflorescences in several Cannabis cultivars even when exposed to long photoperiods. Cannabis sativa L. ‘Suver Haze’ has been reported to develop incomplete inflorescences in North Carolina nurseries using photoperiods of 15 h. The objectives of this study were to investigate the required light intensity and photoperiod to inhibit the flowering of ‘Suver Haze’. In Experiment 1, DE of 1.0, 2.5, 5.8, and 10.3 µmol·m−2·s−1 of photosynthetic photon flux density from incandescent lamps were used to extend the photoperiod of ‘Suver Haze’ from 9 to 15 h. A 9 h photoperiod control was included. The results showed that all DE treatments stopped the full transition to flowering compared to the control; however, all DE-treated plants showed the presence of incomplete inflorescences. In Experiment 2, three photoperiod treatments of 15 h, 18 h, and 21 h were tested. ‘Suver Haze’ under 18 h and 21 h photoperiods did not develop incomplete inflorescences in contrast to plants in 15 h photoperiod. Therefore, a light intensity of at least 1.0 µmol·m−2·s−1 PPFD and an 18 h photoperiod are required to prevent incomplete inflorescences and flowering of ‘Suver Haze’.