Upon irradiation, marine polysaccharides undergo depolymerization, leading to formation of oligosaccharides that elicit various biological activities in plants. Taking a step further on the previously established growth-promoting activity of irradiated sodium alginate (ISA), structural rearrangements in ISA were analyzed using complementary techniques to develop an understanding of the structure-property relationship. The essential oil (EO) of vetiver (Vetiveria zizanioides L. Nash) immensely benefits the perfumery industry, proving itself as an economically important crop. A pot experiment was designed to test the effect of water-soluble ISA fractions on the growth, physiology, and EO production of vetiver. The structural characterization of radiation-induced sodium alginate was carried out using SEM, FT-IR, and UV-Vis spectroscopy. Of the various treatments employed, ISA-120 (ISA applied at 120 mg L-1) proved the best for most of the parameters studied, including fresh and dry weight of plants and photosynthetic attributes. As compared to the control (water-spray treatment), foliar feeding of ISA-120 resulted in an increase of 21.2% in chlorophyll content, while this treatment enhanced the chlorophyll fluorescence by 21.8% at 300 days after transplanting. Application of ISA-120 also increased the EO content by 21.1% and EO yield by 47.6%. Gas chromatography revealed an increase of 30.1% and 92.6% in the values of content and yield of khusimol, respectively, over the control.