The influence of black soldier fly maggots vermiculture zoocompost water extract components on the proliferative activity of root apexes’ meristem and the root system growth of Allium cepa L was studied. Allium-test was used as a biological analysis, approved by International Program on Chemical Safety (IPCS) for monitoring environmental contaminants, substances, and chemicals. The cytogenetic effects, resulting from the action of zoocompost’s water-soluble components and manifesting themselves in abnormalities of mitosis stages, were identified. The «dose-effect» relationship between the water extract components’ content and the mitotic activity of Allium cepa L meristem was determined. The influence of zoocompost water extract components on the elongation zone of root apexes, which affects root system growth, is demonstrated. It is revealed that the biogenic elements of zoocompost water extract components produce a stimulating effect at certain concentrations. The evaluated doses inhibit the proliferative activity of meristem and the growth of the root system. The inhibiting effect is probably due to the increased salts content in the water extract, which causes plasmolysis of cells’ cytoplasm, and alkalosis, caused by the presence of ammonia. It is recommended to take into account the dosage of biologically active substances in zoocompost during the formulation development of fertilizing mixes for plant cultivation.