The regulation of plant growth and developmental processes by carbon dots (CDs) has been frequently reported. However, little is known about how CDs are related to the yield and nutritional quality. In this study, carbon dots, obtained by the hydrothermal method with l-cysteine and glucose, were systematically characterized and applied to lettuces and tomatoes in a hydroponic nutrient solution to comprehensively investigate the mechanism of regulation of plant development by CDs. We found that CDs could accelerate seed germination, promote root and hypocotyl elongation of seedlings by activating the expression of genes encoding aquaporin proteins, and enhance the yield and nutritional qualities of mature plants by promoting the absorption of mineral elements together with the enhancement of photosynthesis. These results provide systematic insights into the mechanisms by which CDs regulate plant development.