Leafy vegetables like lettuce and spinach are prone to significant post-harvest losses during handling and storage. The pre-harvest treatment of crops with biostimulants offers a sustainable strategy for reducing post-harvest losses. Earlier studies focused on the effect of plant biostimulants applied individually. In this study, we studied the efficacy of a combined application of two commonly used plant biostimulants: Ascophyllum nodosum extract (ANE) and humic acid (HA). Interestingly, the combination of both biostimulants improved early growth of lettuce and spinach compared to ANE and HA alone. Among the combinations used in this study, 0.25% ANE + 0.2% HA produced significantly higher fresh and dry biomass in lettuce and spinach compared to the other treatments and the control. Pre-harvest treatment of combination of 0.25% ANE and 0.2% HA significantly reduced the loss of fresh biomass during post-harvest storage. The combination of 0.25% ANE and 0.2% HA reduced lipid peroxidation during storage with an increase in total ascorbate, phenolic, and antioxidant capacity of spinach and lettuce. These results suggest that a combination of ANE and HA reduces post-harvest losses of spinach and lettuce more effectively than when applied individually.