Mentha x piperita volatiles promote Brassica oleracea - A pilot study for sustainable vegetable production

White cabbage was grown in glasshouses with two Mentha x piperita varieties in randomly designed arrangements during spring and autumn 2011/12. The plots were supplemented with one or four Mentha plants of the same variety possessing three main shoots of 7 nodes. Compared to the controls, most pronounced differences were found when the leaves were already exposed to Mentha volatiles during primordium initiation. When applied at sensitive stages of the Brassica seedlings, Mentha volatiles enhanced the productivity and increased the quality and quantity of the aboveground biomass. In another experiment, white cabbage seedlings were exposed to menthone, menthol or their 1: 1 combination. No promoting effect on leaf development or leaf weight was found, but menthol and the combination of menthol/menthone had effects on the shapes of leaves. The stimulatory effects strongly depended on the developmental stage of leaves. Hence, natural mint volatiles lead to other responses of young Brassica plants than single compounds or their combination.