Load-bearing, macroporous cultivation substrate for vertical agriculture: enabled by freeze–thaw processing and green waste–incorporated PVA–agarose composites

The scalability and resilience of vertical agriculture are constrained by the lack of substrates that simultaneously bear mechanical loading, preserve pore connectivity, and maintain a balanced rhizosphere microenvironment. This work develops a load-bearing macroporous substrate through a crosslinker-free freeze–thaw strategy combined with green waste valorization, fabricating physically crosslinked polyvinyl alcohol–agarose composites. The eco-friendly composite exhibits exceptional stability, retaining over 95% of its volumetric integrity under vertical loading. Synergized by freeze–thaw processing and green waste fillers, a hierarchical pore structure is established, with 78% of pores ranging from 0.2 to 50 μm, coordinating water retention (saturated water content >80%) and gas exchange while sustaining rhizosphere oxygen above 19%. Lettuce cultivation confirms significantly improved plant growth. By integrating green waste valorization, low-energy fabrication, and system-oriented design, this study provides a high-performance substrate for vertical agriculture and extends the design paradigm of biomass-based functional composites