Effects of N, P, and K applications alone or in various combinations and ratios were studied on the morphological, physiological, and seed yield attributes and on seed production of calendula. Treatment combinations were control (no N–P–K application), 150 kg ha^-1 N, 80 kg ha^-1 P, 150 kg ha^-1 K, N–P, N–K, P–K, and N–P–K, while in a second experiment, different ratios of N–P–K were compared to determine the best combination and ratio of tested nutrients for optimal growth, quality, yield, and seed production. Plants supplied with N–P–K had vigorous growth, had higher total leaf chlorophyll content, and flowered earlier with greater flower fresh and dry weights, along with improved photosynthetic performance. Plant biomass and seed yield along with leaf N and K were also higher in plants fertilized with N–P–K. In the second experiment, the application of 200–100–100 kg ha^-1 N–P–K resulted in maximum growth, flowering, and seed yield, along with higher photosynthetic activity. Increased leaf area and improved leaf nutrient status were observed at 150–150–150 kg ha^-1 N–P–K, while 200–200–200 kg ha^-1 N–P–K increased stomatal conductance, photosynthetic rate, leaf P, and flower weights. Results demonstrated that a higher level of N along with lower level of P and K are vital for quality calendula flower and seed production.