The effect of different light wavelengths on the germination of lettuce, cabbage, spinach and arugula seeds in a controlled environment chamber

Abstract

The rapid development of vertical farming techniques in recent years has accelerated the necessity for a more thorough investigation into the utilization of artificial lighting. Cultivation in controlled environment systems primarily relies on artificial lighting to provide energy to the plants. One food category that has surged in popularity in recent years is microgreens, which are seedlings consumed during their early stages of growth. Hence, enhancing seed germination and promoting rapid seedling growth can yield significant benefits in this field. The main aim of this study was to analyze how lettuce, cabbage, spinach, and arugula seeds respond under various light spectra and photoperiodic schemes. The selected spectra were UV-A, blue, red, far-red, blue+red, blue+red+far-red, cool-white LED, warm-white LED and darkness, under three different photoperiods: 4, 12 and 24 h. All lighting treatments presented different effects on both seed germination and the morphological characteristics of the seedlings. Lettuce and spinach seeds exhibited robust germination capacity in both darkness and light. However, significant increases in germination rates were observed for cabbage and arugula when exposed to light. In the case of lettuce, a 12 h photoperiod with a blue spectrum led to a 100% germination rate and a leaf area of 77.4 mm². For cabbage, the highest germination rate observed was 70%, which occurred under a blue-red spectrum with a 12 h light cycle. The corresponding leaf area was 44 mm². Spinach exhibited its highest leaf area, reaching 119.16 mm², and a 90% germination rate when exposed to a four h far-red spectrum. Arugula achieved its greatest leaf area, measuring 58.57 mm², and a germination rate of 70% when exposed to a 24 h photoperiod combined with blue-red-far-red lighting. The proper combination of spectra can significantly enhance seed germination rates and guide the plants’ growth towards the desired morphological characteristics.