Influence of urban gardening conditions on the concentration of antioxidant secondary plant metabolites in kale

Abstract

During the COVID-19 pandemic urban gardening became popular across the globe. Leafy vegetables supplement the daily diet and contribute to consumers health. Within the last decade kale (Brassica oleracea var. sabellica L.) gained popularity in urban gardening. However, shading due to unfavourable cardinal directions may reduce plant growth and accumulation of health-promoting secondary plant metabolites such as polyphenols, carotenoids andglucosinolates in kale. We compared authentic urban gardening conditions for kale grown in all four cardinal directions of a residential building. The overall concentration of carotenoids did benefit from sun exposed growing locations, including indoor cultivation behind UV light filtering glass windows, while concentrations of nutritionally important lutein did not differ among the locations and their altered growth conditions regarding abiotic stressors such as sun exposure, temperature, and water consumption. Total concentration of phenolics profited the most from direct sunlight but is severely reduced behind glass windows. Overall, satisfying growth rates of kale were achieved under all applied conditions, encouraging outdoor urban gardening with kale plants even in shaded locations.