The role of irradiated sodium alginate (ISA) as plant growth promoter and in essential oil production was studied in lemongrass, which is a major source of the natural citral. Irradiated sodium alginate has been known as plant growth promoter for various crops. A pot experiment was conducted on lemongrass [Cymbopogon flexuosus (Steud.) Wats.] according to a Complete randomized block design, to study the effect of six levels of ISA viz. 20, 40, 60, and 80 mg L⁻¹ on the basis of growth, content and yield of essential oil and citral content. Growth, biochemical and quality parameters were determined at 120 and 150 days after planting. The effect of ISA application on all the parameters including essential oil production and content and yield of citral was significant at all the growth stages. ISA-60 mg L⁻¹ proved the best for most of the parameters studied. GPC study revealed formation of lower molecular weight oligomers in irradiated samples, which might be responsible for plant growth promotion in the present investigation.