Optimization of Plant Density and Harvest Time to Maximize Volatile Oil Accumulation in Two Aromatic Plants

Volatile oil, mainly extracted from aromatic plants, is widely used in medical, cosmetics, and other industries for its disinfection, sterilization, antioxidant, and other effects. The yield of volatile oil was influenced by plant density and harvest time. Here, two common aromatic plants, Perilla frutescens and Ysphania ambrosioide, were taken as examples to investigate the effects of plant density and harvest time on plant yield-related traits, content, and yield of volatile oil, and the oil yield was determined by steam distillation. Results showed that plant density and harvest time significantly affected the yield and quality of the two plants (p < 0.05). Increasing plant density significantly increased the dry yield and leaf dry yield of P. frutescens, while the dry yield and volatile oil content and yield of Y. ambrosioides significantly decreased, and the maximum value exhibited was at the plant density of 80 cm × 80 cm. In P. frutescens, the maximum volatile oil content was obtained at the plant density of 60 cm × 60 cm, and the maximum volatile oil yield was obtained at the plant density of 30 cm × 30 cm. The yield and volatile oil yield of these two plants increased first and then decreased with the extension of harvest time. The maximum of P. frutescens was in mid-September, and that of Y. ambrosioides was in late October to early November. Our study provides new data for improving plant volatile oil yield and commercial value by optimizing planting density and harvest time and highlights the importance of optimizing planting management mode.