Productivity, oil content, and composition of two spearmint species in Mississippi
‘Scotch’ (Mentha x gracilis Sole) and ‘Native’ (Mentha spicata L.) spearmints are grown in the northern United States, but have not been evaluated in the Southeast. Two-year field studies were conducted in Mississippi at two locations (Verona and Stoneville) to evaluate the effects of N application rate and cut (harvest time) on yields, essential oil contents, compositions, and the yield of individual oil constituents [(–)-carvone, (R)-(+)-limonene, and eucalyptol] in Scotch and Native spearmints. Application of N at 80 and 160 kg/ha increased herbage and oil yields in Scotch, suggesting that commercial Scotch plantations should be provided with 160 kg N/ha. Native spearmint provided similar herbage yields when fertilized with 80 or 160 kg N/ha, but the higher N rate increased oil yields. The essential oil yields in this study were higher than the average oil yields for spearmint grown in the United States during 2008. The essential oil composition of Scotch and Native spearmints grown in Mississippi were similar to the oil produced in other states and other regions in the world. At the Verona site, the average (–)-carvone concentration in the essential oil of Scotch was 68 to 75%, whereas the concentration of (–)-carvone in Native oil ranged from 59 to 62%. At Stoneville, the average (–)-carvone concentration in Scotch oil was 74%, whereas (–)-carvone in Native oil was 68 to 74%. Both Scotch and Native spearmints could be grown as essential oil crops in Mississippi and possibly in other areas of the southeastern United States.