Achillea millefolium is a major medicinal and aromatic herb and has antioxidant, antimicrobial, antispasmodic and antitumor effects in its essential oil. This research was conducted at Floriculture Farm and in the Laboratories of Horticulture Departments, Faculty of Agriculture at Moshtohor, Benha Univ., during 2018/2019 and 2019/2020 seasons to study the effect of foliar spraying at 2000 mg/l with various potassium sources i.e., potassium chloride, potassium citrate, potassium humate, potassium nitrate, potassium silicate, potassium sulphate, monopotassium phosphate and di-potassium hydrogen phosphate on vegetative growth, flowering, essential oil productivity and some chemical constituents of yarrow (Achillea millefolium L.) plants. Results showed that various potassium sources scored highly significant effects on vegetative growth and flowering of A. millefolium L. plant, particularly potassium nitrate followed potassium humate. Moreover, the richest leaf N% was resulted by potassium nitrate, whereas, spraying A. millefolium L. plants with monopotassium phosphate treatment induced the highest values of the percentage of P (%) and total chlorophylls content (%) as well as the maximum K (%), while total carbohydrate content was given by potassium sulphate. In addition, spraying yarrow plant with potassium citrate treatment induced the maximum values of essential oil parameters. Furthermore, the constituents of volatile oil of A. millefolium L. showed 13 components have been recognized. The major components were α-bisabolol oxide B, limonene, carvacrol and chamazulene. Consequently, spraying A. millefolium L. plants with potassium nitrate or potassium humate is recommended, to boost growth, flowering and some chemical constituents, whereas potassium citrate and potassium silicate treatment induced the richest values of essential oils production