Drying and Shade Effects on Native Spearmint Oil Yields and Composition

‘Native’ spearmint (Mentha spicata L.) is one of the two most widely grown spearmints in the United States and in other countries. Recent studies demonstrated its feasibility as cash crop for north central Wyoming. The transportation and energy costs of commercial mint producers can be decreased by drying the spearmint in windrows out in the fields for few days after harvest. And this has been a common practice in the traditional mint producing regions. There is a knowledge gap regarding the effect of drying on ‘Native’ spearmint oil yields and composition. Field and laboratory experiments were conducted in Wyoming to evaluate the effects of drying in days after harvest, DAH (0, 1, 2, 3, 4, 7, 11 DAH) and drying condition (shade and sun) on the essential oil yield, and on the concentrations of beta-pinene, myrcene, limonene, eucalyptol, cis-sabinene hydrate, 4-terpineol, cis-dihydro carvone, cis-carveol, carvone, iso-dihydro carveol acetate, beta-bourbonene, beta-caryophyllene, alpha-humulene/trans-beta-far, and germacrene D in the oil. Treatments did not have significant effect on essential oil yield; the average oil content was 0.25%. The concentrations of myrcene (3% to 3.2% range) and germacrene-D (2.2% to 2.4% range) were greater in the oils from plants dried under a shade compared to the plants dried under direct sun, whereas the concentration of beta-pinene (0.85% to 0.96% range) was greater in plants dried under direct sun. The concentration of carvone (51% to 53% range in the oil) was greater in the plants dried for 1 and 2 days after harvest, and lower in plants dried for 7 days; the rest of the constituents were not significantly different. Drying of ‘Native’ spearmint under direct sun in Wyoming for up to 11 DAH can be practical in an effort to reduce transportation and energy costs without affecting oil yields or composition.