Harvest time affect on the herb yield and essential oil content of lemon thyme (Thymus × citriodorus (Pers.) Schreb)

Lemon thyme (Thymus× citriodorus (Pers.) Schreb) is a perennial sub shrub medicinal plant belonging to the Lamiaceae (Labiatae) family. This plant is a hybrid between Thymus vulgaris and Thymus pulegioides. It has been used as a diaphoretic and for bronchitis. The oil has been found to possess antimicrobial and antifungal activity. This study aims to determine the best harvest time of Lemon Thyme (Thymus × citriodorus) for maximum herbal yield and quantity of essential oil. This research was done at the Botanical Garden of Zardband Company located in the northern Tehran، Iran. Aerial parts of 4-year-old plants were harvested from 10 centimeters of land at 4 stages including: before flowering، beginning of flowering، full flowering and fruit set in the beginning of June to the end of July and then were air dried in the shade. Harvest time had a significant effect on fresh and dry weight of aerial parts in 0. 1% probability level. According to the results maximum amount of fresh and dry weight of aerial parts of T× citriodorus plant were obtained from full flowering and fruit set stages. Based on the results harvest time had no significant effect on the essential oil of T× citriodorus. Although the highest essential oil content (2. 21%) was extracted at beginning of flowering stage but there was no significant difference among different phonological stages. In conclusion، more suitable time for harvesting of T×citriodorus to achieve the maximum yield of essential oil production is at fruit set stage.