Although green (G, 500 to 600 nm) and far-red (FR, 700 to 800 nm) light play important roles in regulating plant growth and development, they are often considered less useful at stimulating photosynthesis than red (R, 600 to 700 nm) and blue (B, 400 to 500 nm) light. Based on this perception, approaches to modifying the transmission of greenhouse glazing materials include (1) conversion of G photons from sunlight into R photons and (2) exclusion of the near-infrared (>700 nm) fraction of sunlight. We evaluated these approaches using simulated scenarios with light-emitting diodes to determine how partial and complete substitution of G with R light and exclusion of FR light affected the growth of lettuce and tomato grown indoors. The substitution of G with R light had little or no effect on fresh and dry mass of tomato. However, with the presence of FR light, fresh and dry mass of lettuce increased by 22–26% as G light was increasingly substituted with R light. In tomato, excluding FR inhibited plant height, leaf area, and dry mass by 60–71%, 10–37%, and 20–44%, respectively. Similarly, in lettuce, excluding FR inhibited plant diameter, leaf length, and dry mass by 15–23%, 23–33%, or 28–48%, respectively. We conclude that the spectral conversion of G-to-R photons can promote plant growth in at least some crop species, such as lettuce, while the exclusion of FR decreases crop growth and yield.

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’.

The global food system is and will be facing many challenges in the coming decades, which will necessitate innovative solutions to address the issues of a diminishing fertilizer supply, an increasing food demand from growing populations, and frequent extreme climates due to greenhouse gas emissions. An advancement proposed is the synthesizing of fertilizer from food waste, here referred to as food waste anaerobic digestate (FWAD). This occurs through the process of anaerobic digestion, where organic matter such as food waste is contained in an anaerobic environment and allowed to be broken down by microorganisms. One of the resulting products is anaerobic digestate, which possesses the necessary nutrients for effective fertilization for crop production. In addition to reducing greenhouse gases and waste in landfills, the replacement of synthetic fertilizers with ones made from food waste would help to alleviate the impacts of the current fertilizer shortage being experienced worldwide, which will be exacerbated by a reducing supply of materials needed for synthetic fertilizer production. In this paper, we discuss the nutrient characteristics of FWAD, and recent studies utilizing FWAD in horticulture and crop production, to advance our understanding of the effectiveness and challenges of using FWAD as a fertilizer. By employing appropriate application methods, such as nitrification, dilution, and amendment, FWAD demonstrates considerable potential as an effective fertilizer for a wide range of leafy greens and some fruiting crops.