Sage (Salvia officinalis L.) is an important aromatic and medicinal plant that is well adapted to dryland conditions and can serve as an alternative crop to cereals worldwide. This study aimed to evaluate how sage responds to different levels of N fertilization and to explore whether morphological and physiological characteristics, as well as vegetation indices, can effectively assess the impact of N fertilization. The study was conducted over two consecutive growing seasons (2022 and 2023) in Greece, using four levels of nitrogen (N) fertilization: 0, 50, 100, and 150 kg N ha-1. Morphological characteristics, such as plant height and leaf area index (LAI), increased by an average of 18% and 30%, respectively, in response to N fertilization compared to the control. The highest increases were observed at 100 and 150 kg N ha-1. Similarly, physiological traits such as chlorophyll meter readings and the quantum yield of photosystem II were higher by an average of 20% and 23%, respectively, at 100 kgN ha-1 relative to the control. Dry matter yield, essential oil content, and essential oil yield were significantly affected by N fertilization. Vegetation indices, including Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI2), and Modified Soil Adjusted Vegetation Index (MSAVI2), also responded positively to N fertilization, showing and average increase of 12%, 42%, and 54%, respectively, under N treatments compared to the control. These findings indicate that N fertilization can significantly enhance sage growth, essential oil content, and yield, offering an effective strategy for optimizing the crop's performance.