Intercropping Lavender and Rosemary in Olive Orchards: Effects of Black Polyethylene Mulch on Vegetative Growth and Essential Oil Characteristics

Intercropping medicinal and aromatic plants (MAPs) with olive trees provides significant economic and ecological benefits in Mediterranean agroecosystems; however, belowground competition for water and nutrients often limits understory plant development. Therefore, the main aim of this two-year field study, conducted in Kilis, Türkiye, was to evaluate the effects of black polyethylene mulch on the vegetative growth and essential oil characteristics of lavender (Lavandula x intermedia) and rosemary (Rosmarinus officinalis L.) cultivated as intercrops between olive rows. The results demonstrated that black polyethylene mulch application significantly enhanced lavender’s vegetative growth, substantially increasing average fresh (1665.5 g for mulched vs. 785.0 g for non-mulched control) and dry biomass (783.5 g for mulched vs. 403.0 g for non-mulched control), plant height (83.37 cm vs. 63.42 cm), and canopy diameter (89.03 cm vs. 71.85 cm) compared to the non-mulched control. Furthermore, lavender essential oil yield improved significantly (5.40% vs. 4.09%), with linalool (30.22%) and camphor (12.69%) identified as the major volatile compounds. For rosemary, mulching positively impacted plant height (42.50 cm vs. 35.00 cm) and shoot length (28.65 cm vs. 22.62 cm), while maintaining a stable essential oil yield (0.40% on average) composed primarily of camphor, eucalyptol, and α-pinene. In conclusion, mulching emerges as a highly effective agronomic practice for mitigating resource competition, promoting vegetative growth, and optimizing essential oil production—particularly for lavender—thereby increasing the sustainability and overall productivity of olive and MAP intercropping systems in semi-arid environments.