Abstract
Beyond producing leafy greens, there is a growing interest in strawberry production on indoor vertical farms. Considering that sole-source lighting is one of the most important components for successful indoor crop production, we investigated how photosynthetic photon flux density (PPFD) and the photoperiod of sole-source lighting affected plant growth, flowering, and fruit production in strawberry 'Albion.' Bare-rooted strawberry plants were grown in deep water culture hydroponics inside an indoor vertical farm at 21 °C under white + blue + red light-emitting diodes at a PPFD of 200, 300, or 450 µmol∙m(-2)∙s(-1) with a 12-h or 16-h photoperiod. Under both photoperiods, increasing PPFD from 200 to 450 µmol∙m(-2)∙s(-1) linearly increased crown diameter by 18-64%, shoot fresh and dry mass by 38-80%, and root fresh and dry mass by 19-48%. Under a PPFD ≥ 300 µmol∙m(-2)∙s(-1), root fresh and dry biomass increased by 95-108% and 41-44%, respectively, with an increasing photoperiod from 12 to 16 h. In addition, increasing the photoperiod from 12 to 16 h accelerated flowering by 17-21 days under a PPFD ≥ 300 µmol∙m(-2)∙s(-1) and first fruit harvest by 17 days at a PPFD of 450 µmol∙m(-2)∙s(-1). Regardless of PPFD, strawberry fruit production (g·m(-2)·month(-1)) increased by 372-989% under a 16-h photoperiod in comparison to under a 12-h photoperiod. In contrast, there was little effect of PPFD on fruit production. Our results suggest that increasing the PPFD or photoperiod can increase strawberry plant growth, but increasing the photoperiod can have a dominant effect on increasing early fruit production in strawberry 'Albion'.