Persistent accumulation of non-biodegradable plastics in agricultural soils highlights the need for sustainable alternatives to conventional mulch films. Here, we report high-strength biodegradable mulch films fabricated from lignocellulose nanofibers (LCNFs) obtained from fallen leaves, an abundant non-edible biomass. LCNFs were extracted and blended with cellulose nanocrystals (CNCs), poly(vinyl alcohol) (PVA), and glycerol (Gly) using water as the sole processing medium. The resulting lignin-containing all-nanocellulose/PVA (LANC/PVA) films were formed via evaporation-induced self-assembly and exhibited low water vapor permeability, strong UV shielding, and effective moisture retention. Soil incubation confirmed rapid biodegradation and no detectable phytotoxicity, supporting their compatibility with seed germination and early plant growth. These results position leaf-derived films as promising eco-friendly mulch materials for sustainable plasticulture.