EFFECT OF HARVEST DATE ON THE YIELD AND QUALITY OF THE ESSENTIAL OIL OF PEPPERMINT

A field experiment was conducted from 1989 to 1991 on a Fox loamy sand soil to study the effects of harvest date on selected agronomic, phys ical and chemical characteristics of peppermint (Mentha piperita L.). Plant biomass and essential oil yields increased throughout the season to a maximum in very late August to early September. Menthol, neoment hol, and menthyl acetate concentrations increased in the essential oil with plant development. The amount of menthone and isomenthone was hi ghest in immature plants. The concentrations of menthofuran and pulego ne in the essential oil corresponded to the amount of flower bloom in the peppermint. Changes during the season in the concentrations of pip eritone, terpinene-4-ol, alpha-terpineol, 1,8-cineole, limonene, gamma -terpinene, terpinolene, alpha-terpinene, alpha-pinene, beta-pinene, 3 -octanol, beta-myrcene, Linalool, sabinene, caryophyllene and Germacre ne-D were typically quite small. In general, these preliminary results indicate that peppermint can be grown successfully on the coarse-text ured soils ot Ontario.