Optimising Sowing Density for Microgreens Production in Rapini, Kale and Cress

Microgreens represent a valuable agrifoods niche. Their cropping cycle is shorter than that of baby leaf greens, but the sowing density is typically much higher, and this has important cost implications for the grower. The current research demonstrates that the choice of sowing density strongly influences yield, as well as developmental stage and other quality parameters. Results also depended on the choice of the species and landrace. Considering the cost of seed, the option of accessing locally available landraces becomes particularly intriguing, again with relevant implications in choosing seed density. Rapini (landraces Cima grande and Fasanese), kale (landraces Barese and Altamura), and commercial cress were grown in an indoor environment. The effects of the three sowing densities (from 3 to 5 seeds∙cm−2) and the growing cycle (earlier harvest, 11 days from sowing, or later harvest, 14 days from sowing) on the microgreen yield and quality were studied. Sowing density affected yield (+19% at highest vs. lowest density), dry matter (but only with a longer cycle, and variable by landrace, with Fasanese rapini landrace 7% more than the Cima grande landrace), developmental stage, and soil coverage. The effects of sowing density can be modulated by cycle duration. Crop heights were 25% and 44% greater for the longer cycle of the Cima grande and Fasanese rapini landraces, respectively. In conclusion, the choices of the species/landrace and seed density must be carefully evaluated given costs and outcomes, with potential for the production of different final products (e.g., microgreens at earlier or later stages, other characteristics) and also for control over costs.