Abstract: This study aimed at researching suitable transplanting period and environmental conditions for Cotoneaster hjelmqvistii plantlet in vitro. In green-house the C. hjelmqvistii plantlets in vitro were transplanted with lump three times in term from March end to May end and the survival rate of the plantlets was observed. The stem length of the C. hjelmqvistii plantlet was respectively measured at 7 o’clock, 12 o’clock and 17 o’clock in one day. The result show that the survival rate of the C. hjelmqvistii plantlet in vitro transplanted on April 29th and May 29th were 93.8% and 96.1%, which were higher than that of the plantlet transplanted on March 30th (85.9%); During the observation period the stem growth of the C. hjelmqvistii plantlet from 12 o’clock to 17 o’clock was obvious higher than the growth from 7 o’clock to 12 o’clock; The stem of the C. hjelmqvistii plantlet grew obviously above 15 ℃ and grew more quickly in 25-30 ℃. Temperature is the determinative fact in transplanting plants. In green-house the suitable transplanting time is the period during which the minimum temperature in a day is above 15 ℃ and the maximum temperature in a day is under 30 ℃, which is the period about from the last ten-day period of April to the end of May in Tianjin.

Key words: Cotoneaster hjelmqvistii, plantlet in vitro, transplanting period, environment, survival