Depolymerised carrageenan enhances physiological activities and menthol production in Mentha arvensis L.

► Irradiated carrageenan (IC) could elicit plant growth promoting activities in plants. ► Foliar spray of IC improved growth, yield and quality attributes of Mentha arvensis. ► The IC spray at 80 mg L−1 gave the highest values for most of the attributes studied. ► Foliar spray of IC at 100 mg L−1 did not further improve the attributes studied. ► The spray of unirradiated carrageenan and deionized water had no significant effect.