This study aimed to observe the growth of mustard plants (Brassica juncea L) with liquid organic fertilizer from rice washing wastewater with various concentrations. This study used an experimental method with a completely randomized design (CRD) consisting of 4 treatments and 5 replications. Parameters observed were seedling acceleration, plant height, number of leaves, and leaf length. Control treatment concentrations (P0) (without adding POC rice washing water), P1 (5 ml rice washing water / 0.5 L water / day), P2 (15 ml rice washing water / 0.5 L water / day), and P3 (25 ml of rice washing water / 0.5 L of water / day). The data obtained will be analyzed using analysis of variance (ANOVA) with a confidence level of 95%. Based on the research data obtained, that the provision of rice washing wastewater affects the growth of plant height and number of leaves. However, it did not affect seedling acceleration and leaf length. The average seeding acceleration occurred 3 days after planting with each treatment and repetition during the study period. In terms of plant height, the control treatment (P0) had the highest growth (16.36 ± 1.48 cm), while the 25 ml/L treatment (P3) had the lowest average (11.50 ± 1.25 cm). The control treatment (P0), namely (6.66 ± 0.57 cm) was the growth in the highest number of leaves, while P3 with 25 ml/L was the lowest average number of leaves obtained. The control treatment (P0) with the longest leaf length growth was (5.93 ± 1.65 cm), and (P3) 25 ml/L, namely (3.80 ± 0.70 cm) was the lowest average leaf growth.