It is challenging to fabricate degradable poly(vinyl alcohol) (PVA)-based plastics that can be used in watery environments because PVA is soluble in water. In this study, PVA-based supramolecular plastics with excellent degradability in soil and high mechanical strength in watery environments are fabricated by the complexation of vanillin-grafted PVA (VPVA), hydrophobic humic acid (HA), and Fe ions (hereafter denoted as VPVA-HA-Fe complexes). Large-area PVA-based plastics can be easily prepared from a solution of VPVA-HA-Fe complexes using a blade-coating method. The high-density of hydrogen bonds and coordination interactions, as well as the reinforcement of self-assembled Fe -chelated HA nanoparticles, facilitate the fabrication of PVA-based plastics with a breaking strength of ≈85.0 MPa. After immersion in water at room temperature for 7 d, the PVA-based plastics exhibit a breaking strength of ≈26.2 MPa, which is similar to that of polyethylene in its dry state. Furthermore, owing to the reversibility of the hydrogen bonds and coordination interactions, the VPVA-HA-Fe plastics are recyclable and can be conveniently processed into plastic products with desired shapes. After being placed under soil for ≈108 d, the PVA-based plastics are completely degraded into nontoxic species without requiring manual interference.