Abstract <p>The flower industry generates substantial amounts of stem and leaf waste from non-standard or unsold flowers, which are often discarded as waste despite their potential as a renewable biomass resource. In this study, we investigated the upcycling of flower stem and leaf powder into cellulose nanofibers (CNFs) using two distinct isolation methods: TEMPO-mediated oxidation to produce TEMPO-oxidized CNFs (TCNFs) and mechanical disintegration to produce mechanically disintegrated CNFs (MCNFs). The morphology of the obtained nanofibers was examined using atomic force microscopy and field-emission scanning electron microscopy, revealing that TCNFs exhibited thinner, more uniform fibrils with higher aspect ratios, whereas MCNFs displayed slightly thicker fibers with greater heterogeneity. Rheological measurements indicated shear-thinning and thixotropic behavior for both CNF suspensions, with viscosity primarily dependent on the concentration rather than the disintegration method. Solid-state nuclear magnetic resonance (NMR) and Fourier transform infrared analyses confirmed the removal of hemicellulose and lignin in both samples, while TCNFs exhibited a characteristic peak for carboxyl groups at 175&#xa0;ppm and 1605&#xa0;cm⁻¹, reflecting TEMPO oxidation. NMR analysis revealed no significant differences between the crystallinity indices of the two CNF samples. These findings demonstrate that flower stems and leaves—an underutilized form of floral waste—can be effectively converted into CNFs with distinct structural and chemical characteristics, depending on the isolation strategy. This study highlights the potential of floral waste valorization as a sustainable technique to obtain nanocellulose for high-value applications.</p> Graphical abstract <p></p>