Floating farming systems have emerged as a promising adaptive technology for rice cultivation in lowland swamps, where chronic waterlogging renders conventional agriculture challenging. These systems typically employ local aquatic vegetation as a growth substrate; however, a comprehensive evaluation of its agronomic potential has been lacking. This study quantifies the efficacy of this aquatic vegetation medium in supporting the growth and yield of two rice varieties, Ciherang and NutriZinc, within a floating farming system. The varieties were cultivated on floating rafts, and a comprehensive analysis of the growth medium and plant production was conducted at 120 days after planting. Results demonstrated that the substrate provided an optimal physicochemical environment for rice. The pH was ideal for both Ciherang (5.78–6.54) and NutriZinc (5.98–6.87). Essential nutrients were available at sufficient levels: phosphorus (81–167 mg P kg⁻¹) and nitrogen in the forms of NH₄⁺ (68–148 mg N kg⁻¹) and NO₃⁻ (23–67 mg N kg⁻¹). Furthermore, supportive levels of organic carbon, total nitrogen, and exchangeable cations (K, Ca, Mg) were recorded. These favourable conditions directly translated to high yields, with Ciherang and NutriZinc producing 271.3 g plant⁻¹ and 443.1 g plant⁻¹, respectively—a yield comparable to conventional cultivation. This study confirms that aquatic vegetation from lowland swamps is a highly effective growth medium, capable of supplying optimal nutrient levels to sustain high rice productivity, thereby validating floating farming as a viable and productive solution for waterlogged environments.