High demand of food for rapidly increasing population requires novel but ecofriendly fertilizers. Green reducing and capping agents are being explored to minimize production cost and toxicity of chemicals in synthesis of nanoparticles (NPs) which could be used to increase the production of crops and plants. In present research, Zinc Oxide Nanoparticles (ZnO NPs) are produced by employing an eco-friendly, simple and efficient green route using peel extract of Citrus reticulate. The optical properties of green synthesized ZnO NPs are explored by UV-Visible and Photoluminance spectroscopies where NPs presented 3.21 to 3.13 eV band gap. The morphology and purity of the ZnO NPs are analyzed by scanning electron microscopy (SEM), X-ray diffraction technique (XRD) and energy dispersive X-ray spectroscopy (EDX), respectively. The spherical like ZnO NPs having 23-90 nm size exhibited hexagonal structure with 8.89 to 8.62 nm crystallite size. Fourier transform infrared spectroscopy (FTIR) explores the existence of specific functional groups which are responsible for stabilization, capping and reduction during synthesis of nanoparticles. The green synthesized ZnO NPs are tested for seed germination of Brassica nigra (black mustard) seeds at standard temperature and pressure. The activity shows that germination percentage of the Brassica nigra seeds is enhanced 100% and seedling vigor index 16.45 after treatment with ZnO NPs and can be controlled by the concentration of NPs. Therefore, it can be expected that ZnO NPs can serve as the cost effective and ecofriendly nano-fertilizers in agriculture.