Cannabis sativa L. is an annual, short-day plant, such that long-day lighting promotes vegetative growth while short-day lighting induces flowering. To date, there has been no substantial investigation on how the switch between these photoperiods influences yield of C. sativa despite the tight correlation that plant size and floral biomass have with the timing of photoperiod switches in indoor growing facilities worldwide. Moreover, there are only casual predictions around how the timing of the photoperiodic switch may affect the production of secondary metabolites, like cannabinoids. Here we use a meta-analytic approach to determine when growers should switch photoperiods to optimize C. sativa floral biomass and cannabinoid content. To this end, we searched through ISI Web of Science for peer-reviewed publications of C. sativa that reported experimental photoperiod durations and results containing cannabinoid concentrations and/or floral biomass, then from 26 studies, we estimated the relationship between photoperiod and yield using quantile regression. Floral biomass was maximized when the long daylength photoperiod was minimized (i.e., 14 days), while THC and CBD potency was maximized under long day length photoperiod for ~42 and 49–50 days, respectively. Our work reveals a yield trade-off in C. sativa between cannabinoid concentration and floral biomass where more time spent under long-day lighting maximizes cannabinoid content and less time spent under long-day lighting maximizes floral biomass. Growers should carefully consider the length of long-day lighting exposure as it can be used as a tool to maximize desired yield outcomes.
Allotment food gardens represent important sources of food security for urban residents. Since urban gardeners rarely receive formal agricultural education and have extremely limited space, they may be relying on readily available gardening advice (e.g., seed packet instructions), inventing cultural strategies that consider inter-specific competitive dynamics, or making poor planting decisions. Knowledge of garden crop diversity and planting arrangements can aid in designing strategies for productive urban gardens and food systems. We surveyed 96 individual plots in 10 allotment gardens in the Toronto region, assessed crop diversity within gardens and recorded planting practices used by urban gardeners by measuring the proximity of individual plants relative to similar or different crop species. We also compared planting densities used by urban gardeners with those recommended by major seed distributers. Collectively, Toronto urban agriculture contributes substantially to urban plant diversity (108 crops), but each plot tends to be relatively depauperate. Carrots and lettuce were three to five times more likely to be planted in clusters than intermingled with other crops (P < 0.05); whereas gardeners did not appear to use consistent planting arrangements for tomatoes or zucchini. Gardeners tended to plant tomatoes and zucchini 56–62.5% more densely than recommended by seed distributers (P < 0.001), whereas they planted 147 times fewer carrots in a given area than recommended (P < 0.05). Furthermore, neither crop planting density nor crop diversity changed with plot size. The planting arrangements we have documented suggest gardeners using allotment plots attempt plant densely in extremely limited space, and are employing cultural strategies that intensify competitive dynamics within gardens. Future research should assess the absolute and relative effect of altered cultural practices on yield, such that any modifications can be prioritized by their impact on yield.
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