Peppermint Productivity and Oil Composition as a Function of Nitrogen, Growth Stage, and Harvest Time

Abstract

The commercial production of peppermint ( Mentha × piperita L.) is concentrated in more northern latitudes worldwide (north of the 41st parallel), including the United States. This 2‐yr field study in Mississippi evaluated the effect of N (0, 80, and 160 kg/ha), growth stage (bud formation and flowering), and harvest time or cut (first cut in mid‐July, second cut beginning of October) on peppermint yields, oil content, and composition. Biomass and oil yields were higher from the first cut than from the second. Overall, N increased biomass and oil yields. Contrary to literature reports that peppermint requires long days north of the 41st parallel to reach flowering, peppermint in Mississippi (at 34°43′22″ N lat) did reach flowering. The average oil yields at bud formation and at flowering were 165 and 122 kg/ha, respectively, and were greater than the average peppermint essential oil yields for the United States in 2008. Generally, (–)‐menthol concentration in the oil from the 2007 harvest was lower than in the oil from the 2008 harvest. The average (–)‐menthol concentration in the oil from the fertilized plots harvested at flowering in 2008 was 43 to 46%, but (–)‐menthol in the other treatments was below 37%. Our results suggest the first harvest in Mississippi should be delayed until the end of July to promote conversion of (–)‐menthone to (–)‐menthol. Peppermint could provide two harvests per growing season under the Mississippi climate, with oil yields and composition similar to those from other peppermint production regions.