Bio-based materials are emerging as an innovative solution for vegetation restoration thanks to their porous structure, high water absorption and low environmental impact. To improve the water retention capacity of miscanthus fibre mortar, the effects of superabsorbent polymer (SAP) content (0.1 wt%, 0.2 wt% and 0.3 wt%) on the physical characteristics, mechanical strength, microstructure, plant growth performance, drought resistance and the mortar properties after planting are investigated in this study. The results show that the addition of low SAP content (0.1% and 0.2%) enhances the water retention capacity, which can absorb 67-71% of water by its weight at 0.5 hand then retain 21-27% of absorbed water until 11 days. The SAP has a significant effect on the early germination and rooting of plant seeds. The plants grow well on the mortars SAP0.2% and SAP0.3% surface after germination, showing a more number of plants, compared to the mortar Ref. Moreover, as the SAP content increases, the plant cover percentage shows a gradually increasing trend. However, a high plant cover percentage exhibits a negative impact on plant height, leaves and root development for the individual plant. In addition, plant roots are prone to grow laterally, and plant roots can penetrate deeply into the mortar matrix. The increased water absorption of the miscanthus fibre mortar is an effective method to improve plants' resistance to drought climatic conditions. The use of 0.2% SAP is preferred for improving plant growth adaptability in sustainable greening projects, considering good water retention ability and without sacrificing its strength.