Natural biostimulants like seaweed extracts (SWE) have significantly increased crop productivity. However, studies exploring the effect of SWE on medicinal plant productivity are scant. The present study aimed to enhance the root biomass and reserpine content in Rauvolfia serpentina by foliar application of SWE. Using a randomized block design, a field experiment with R. serpentina was established, and seven treatments of SWE (3–21 %) were applied through a foliar spray. Data on growth, above-ground biomass, and root biomass of mature harvested plants were recorded, while dried roots were analyzed for physicochemical, total alkaloid, and reserpine content. Among the treatments, the application of SWE at 6 % demonstrated notably higher CD (13.20 cm) and plant spread (18.80 cm²) compared to other treatments, being comparable to SWE at 3 % (CD: 12.67 cm, plant spread: 18.42 cm²). Similarly, lower SWE doses significantly improved fresh-weight root biomass by 18.16–39.17 % and dry-weight root biomass by 16.53–58.23 % compared to the control. Physicochemical and alkaloid content in the root was increased by lower SWE doses and found safe for drug application as per quality standards. SWE @3 % increased the reserpine content significantly by 111.11–137.77 % over control, which is a good finding for commercial drug production. Therefore, the present study recommends the foliar application of low doses of SWE (3–6 %) for organic cultivation of economically important R serpentine for better root biomass and reserpine production, which would be safer in use and support export trade in the root.