Plant waste is a huge source of natural fibers and has great potential in the field of reinforced polymer composites to replace the environmentally harmful synthetic composites. In this study, fibers were extracted from water hyacinth (WH) petiole and sugarcane bagasse (SB) to make nonwovens by wet-laid web formation, and reinforced on the polyester (P) and epoxy (E) resins to make four types of composites namely, water hyacinth nonwoven reinforced epoxy (WH + E), water hyacinth nonwoven reinforced polyester (WH + P), sugarcane bagasse nonwoven reinforced epoxy (SB + E) and sugarcane bagasse nonwoven reinforced polyester (SB + P) composites. Water repellent (WR) on the nonwovens and gamma radiation (GR) on the composites were applied to improve the hydrophobicity and mechanical properties, such as tensile strength (TS), elongation at break and tensile modulus (TM) of the composites. The morphological structure of the fiber surfaces and tensile fractures were analyzed by SEM. FTIR spectra showed changes in functional groups before and after treatment. XRD analysis exhibited an increase in crystallinity for gamma-irradiated composites and a decrease in crystallinity for WR-treated composites compared to untreated composites. The SB composites (SB + E, SB + P) and polyester composites (WH + P, SB + P) showed higher water absorbency and lower mechanical properties than the WH composites (WH + E, WH + P) and epoxy composites (WH + E, SB + E), respectively. Hydrophobicity improved significantly by approximately 57\% (average) at a concentration of 10\% WR. However, TS and TM were reduced by approximately 24\% at the same concentration. Thus, 5\% WR is considered an optimum concentration due to the very low deterioration of TS and TM (<10\%) but significant improvement in hydrophobicity (similar to 39\%) at this dose. On the other hand, GR treatment significantly improved TS, TM and hydrophobicity by 41, 32 and 25\%, respectively, and decreased Eb\% by 11\% at a dose of 200 krd. However, mechanical properties and hydrophobicity deteriorated with further increase in dose at 300 krd. Thus, 200 krd is considered the optimum dose of GR.