Polyurethane Foam as a model platform for evaluating properties of soilless growing media

The increasing adoption of hydroponics and soilless cultivation techniques in food production has increased the demand for novel soilless growing media, presenting a unique opportunity for the development of customised media. Given the wide variety of crops and cultivation techniques used in soilless systems, optimising the physical properties of novel media for specific crops and systems presents both a challenge and an opportunity, as many growing media components provide only a single set of physical properties to work with. Polyurethane foams (PUFs), a promising soilless growing media, offer flexibility, as their formulation chemistry can be adjusted to produce foams with a diverse range of physical properties. This adaptability enables the tailoring of foams for specific crops and systems, providing valuable insights into optimised growing media “recipes” for various conditions. In this study, we examined 10 distinct PUF formulations with a range of physical properties through germination and growth trials. A preliminary investigation into whether physical or chemical characteristics of these media influence disease susceptibility was conducted by inoculating tomato plants with Pythium sp . An initial germination trial using lettuce and tomato identified four PUF formulations as unsuitable. A subsequent small scale growth trial demonstrated that the remaining six formulations performed comparably to mineral wool (MW) in terms of yield. Three of these formulations, which showed the highest yields, were then tested in yield trials for lettuce and pak choi in a nutrient film technique (NFT) system and for tomato using a dripper-fed system. Results indicated that two PUF formulations surpassed MW in vegetative yield in tomato trials, while two PUF formulations matched MW in lettuce yield in NFT trials. However, pak choi plants grown in foam displayed slightly lower yields than those in MW, although differences were not significant. All foam samples suppressed Pythium , as evidenced by no observed reductions in germination rates or seedling mass when compared to the uninfected samples, warranting further investigation into disease suppression potential. Overall, these yield results underscore that a “one size fits all” approach to soilless media formulation is inappropriate; rather, media should be optimised according to both hydroponic technique and crop type to maximise yields and other benefits. This study demonstrates that PUFs offer a valuable platform for developing tailored growing media "recipes" aligned with specific crop and system requirements.