Growth, Herb, and Essential Oil of Marrubium vulgare as Affected by Phenological Stages and Planting Date

The objective of this study was to investigate the effect of planting dates and harvesting at different developmental stages on growth, herb yield, and essential oil content and composition of Marrubium vulgare grown under Egyptian conditions. Marrubium vulgare seeds were sown in the nursery on three different dates: March 15, April 1, and April 15. After two months, seedlings were transplanted into the field. Plants from each planting date were harvested at three developmental stages: pre-flowering/vegetative stage, full-flowering, and post-flowering/seed-forming stage. Essential oil was obtained by hydrodistillation, and its chemical composition was analyzed using GC-MS. Compounds were identified based on their mass spectra and literature. Marrubium plants cultivated early on March 15th exhibited the highest plant height, number of branches, and fresh and dry weights compared to plants cultivated later on April 1st or April 15th. Harvesting at the late flowering stage resulted in the highest values for these parameters. Regarding essential oil production, plants cultivated early on March 15th or April 1st and harvested at the full flowering stage yielded the highest essential oil percentage and yield compared to those harvested early before the flowering stage. Cultivation date and phenological stages caused quantitative and qualitative changes in the essential oil components. About 32 compounds were identified, with carvacrol (16.8-41.75%), p-cymene (6.1-17.25%), thymol (0.63-23.87%), γ-terpinene (3.76-17.89%), and β-phellandrene (6.19-14.12%) being the major compounds. It can be concluded that cultivating Marrubium plants early on March 15th, combined with harvesting at the full flowering stage, is essential for maximizing herb and essential oil yield.