The potential of using spent mushroom substrate (SMS) as inoculant carrier and organic amendment on the growth of Hibiscus sabdariffa was evaluated. SMS, peat and vermiculite were mixed with plant growth promoting bacteria (PGPB) isolate Bacillus amyloliquefaciens. Different treatments were applied in the cultivation of H. sabdariffa. We found that application of NPK fertilizer, SMS based inoculant, and peat based inoculant significantly promoted plant growth and chlorophyll content compared to other treatments. SMS based inoculant was the best treatment for increasing biomass and chlorophyll content, followed by NPK fertilizer. In addition, application of SMS inoculant or only SMS as soil amendment showed a significant improvement in soil properties including soil NPK, organic matter, soil PGPB and soil enzyme (i.e. soil fluorescein diacetate and dehydrogenase) as well as peat inoculant application. Our results suggested that SMS could be considered as an alternative low-cost, potential carrier in biofertilizer production or soil amendment for providing soil nutrients and recovering soil fertility in farming.