This paper presents an investigation of the capacity of four different plants to remove and assimilate ferri-cyanide at different pH conditions. Detached roots of weeping willows ( Salix babylonica
L.), rice ( Oryza sativa
L. cv. JY 98), soybean ( Glycine max
L. cv. WH) and maize ( Zea mays
L. var. HK) were hydroponically exposed to ferri-cyanide in a closed system at 25 ± 0.5°C for 24 h kept under darkness. Almost all applied ferri-cyanide was in the complex form in the hydroponic solution at pH ≥ 7.0 in the absence of light, while dissociation of ferri-cyanide to free cyanide and iron in solution was detected at pH ≤ 6.5. All plant species used were found to be able to remove and assimilate ferri-cyanide efficiently. The uptake and assimilation rates appeared to be inversely related to the pH, in which positive effects were observed at pH 6.0 and 6.5. Remarkable decreases in the assimilation rates were found at pH 8.0. Results presented here suggest that changes in solution pH have a substantial influence on not only the speciation of ferri-cyanide in the plant growth media, but also the uptake and assimilation mechanisms of ferri-cyanide by plants.