‘Bartzella’ is an excellent variety of Itoh peony ［Paeonia Itoh group］ because it can be planted in pots offseason. Growth and development, flowering quality, and related physiological indexes were evaluated following application of watersoluble fertilizer (NPK=202020+TE) (0, 0.8, 1.2 and 1.6 g·L^-1) in pots planted with ‘Bartzella’ in the south of China in winter at the initial stage of stem elongation. The results showed that: (1) fertilization significantly increased growth and nutrients of various organs of the plants. (2) Contents of chlorophyll, soluble protein and soluble sugar in leaves, stem length and diameter, bud diameter, and nitrogen and potassium levels in various organs increased with increasing dose. Bud diameter of the plants treated by 1.2 and 1.6 g·L^-1 increased by 4.4% and 7.7% compared with the control (P<0.05), cultivation time decreased by 4.45 and 2.65 d, and the best viewing period increased by 5.08 and 1.70 d, respectively. (3) Flower diameter and flower formation rate per plant increased by 16.0% and 13.5% (P<0.05), respectively, and contents of flavonoids and carotenoids and yellowness of petals increased (P<0.05). Our results show that appropriate concentration of watersoluble fertilizer can significantly coordinate development of stems, leaves and flowers of offseason cultivated ‘Bartzella’ and can be used in potted cultivation. The dose of 1.2 g·L^-1 is suggested.