As entrepreneurs look to find new ways to shorten the gap between farm and table in urban communities, many are considering vertical farming as an answer to the problem of limited growing space. The aim of this experiment is to determine the optimal harvest time in weeks for vertically grown, hydroponic kale (Brassica oleracea var. acephala cv. ‘Toscano’) based on morphological data, phytonutrient concentrations, energy, and yield. After a four-week germination period, kale was grown for up to eight weeks and harvested at eight different stages of growth, based on the number of weeks spent in the vertical system. When harvested, morphological parameters were measured, and samples were collected to analyze mineral nutrient content. Electrical Energy usage data was collected and presented as: Lighting, HVAC, and Other. Data was analyzed as a Randomized Complete Block Design with three blocks. Mean plant height, fresh leaf mass, and leaf dry mass all increased with growth stage, with the largest plants being observed at stage eight. Additionally, the greatest mean quantity of dead, diseased, or unconsumable leaves of 3.27 leaves per plant was observed at stage eight. Mineral nutrient concentrations of calcium, sulfur, and manganese increased through seven weeks (stage seven), after which a decrease was observed in stage eight. Decreases in concentration during stage eight was also observed for phosphorus, potassium, and magnesium, with negligible differences in the younger stages. No differences in energy data existed for the daily mean lighting, HVAC, and Other electrical consumption across all eight stages. Harvest data collected indicates that plants should be harvested prior to stage eight to maintain mineral nutrient content and minimize dead leaves and should be considered with total energy consumption to optimize farm productivity, energy efficiency, and nutritional content of plants. Further analysis of other primary and secondary metabolites alongside total energy consumption cost is necessary to identify the best stage of harvest maturity and nutritional quality for consumers relative to energy usage and production cost.
