The reduction and reuse of composting leachate is an issue of importance in the field of decentralized solid waste management. In this study, composting leachate from source-separated food waste was treated and subsequently used as liquid fertilizer to irrigate Impatiens (Impatiens balsamina). The leachate was altered by adjusting storage time and dilution, and through addition of microbial inocula. For each test case, the effects of irrigation were monitored by analyzing the Impatiens extension degree, numbers of leaves and flowers, dry weight, and photosynthetic pigment content to assess fertilizer efficiency. The main results obtained revealed that the addition of microbial inocula and lengthening of storage times may lower COD concentrations, adjust pH value and maintain a comparatively high level of nutrient contents. By adding microbial inocula, a COD concentration of 9.6% and BOD5 concentration of 6.7% were obtained for non-treated leachate with the same storage time. COD concentrations in leachate decreased to 69.4% after 36weeks storage. Moreover, composting leachate promoted growth of Impatiens. The dry weight biomass of Impatiens irrigated using treated diluted leachate was 1.15–2.94 times that obtained for Impatiens irrigated using tap water. Lastly, following the irrigation of Impatiens over a short period, soil did not accumulate VOCs and heavy metals to levels exceeding relative standards. Further research on heavy metal and salinity accumulation in plants should be undertaken to meet the needs of large-scale applications.