Although several studies have examined the synthesis of CuO NPs using plant extracts, the use of yerba mate (Ilex paraguariensis) in this process has not yet been explored. Rich in bioactive compounds, including flavonoids and polyphenols, yerba mate exhibits strong antioxidant capacity, which can aid in stabilizing NPs and influencing their physicochemical properties. Furthermore, while CuO NPs have been extensively studied for their antimicrobial properties and role as a micronutrient source, their direct effects on seed germination and early plant growth remain poorly understood, particularly when synthesized using a green approach. Moreover, the impact of synthesis conditions on NPs formation and properties remains insufficiently explored, underscoring the need for further investigation into how reaction parameters influence nanoparticle characteristics. Another gap in the field is the investigation of the mechanism of formation of NPs from green sources to understand the interaction of the bioactive in the extract and their influence on the properties of the NPs. In light of this, we propose an innovative approach utilizing yerba mate extract for the green synthesis of CuO NPs, eliminating the need for aggressive chemical agents and promoting a method aligned with sustainable chemistry principles.