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<i>Miscanthus × giganteus</i> (<i>Miscanthus</i>) is a warm-season perennial grass grown for bioenergy feedstock production. Nitrogen (N) fertilizer management is crucial for the sustainability of <i>Miscanthus</i> production. In our two-year study (2018 and 2019), we investigated the role of vegetation indices (VIs) in evaluating N fertilization (0 N, 56 N, 112 N, and 168 N kg ha⁻¹) impacts on <i>Miscanthus</i> biomass yield and stand health. The flight campaigns were conducted early, middle, and late during the summer growing season. Among the VIs, mid-summer growing season NDRE provided the best prediction of fresh biomass (R² = 0.87 and 0.97) and dry biomass (R² = 0.89 and 0.97) in 2018 and 2019, respectively. The VIs generally showed that it was possible to distinguish between 0 N and 168 N treatments, but neither 0 N and 56 N kg ha⁻¹ nor 112 N and 168 N kg ha⁻¹ could be separated. The results from this study highlight the importance of moderate application of N (112 kg N ha⁻¹) in improving and maintaining the stand health and biomass yield of <i>Miscanthus</i> over time and suggest that mid-summer growing season VIs, NDRE in particular, can be useful for assessment of <i>Miscanthus</i> stand health and biomass yield.