Objective To find out the growth rhythms of the seedlings of Chinese unique precious fast-growing timber species Toona sinensis, for raising seedling quality and tending effect of young stand.

Method The seeds were collected from 14 representative locations of T. sinensis distribution area. Seedling growth was observed continuously for one year. Logistic equations were used to fit the growth in seedling height and ground diameter, and seedling growth stages were divided.

Result The growth in seedling height of different provenances had three stages. Slow growth period was from January to April. Rapid growth period was from mid-May to the end of September, followed with another slow growth period. The "Slow-Fast-Slow" growth process showed "S" type rhythm. The growth rhythm of the ground diameter also showed as "S" type, whereas the beginning time of rapid growth period was generally earlier than that of height growth, and the duration of rapid growth was generally longer by continuing until mid- or late October. There were significant differences in growth rhythms among seedlings of different provenances. The rapid growth period of southern provenances was from April to September, lasting for a long time. The rapid growth period of northern provenances was relatively short and was mainly in June and July. The ground diameters of southern provenances continued to grow fast in August and September. However, the northern provenances step into a slow growth period in July or August, and in general stopped growing after mid-September.

Conclusion Northern provenances are not suitable for cultivation in Guangdong. There are high precisions in the logistic equations used to fit growth in height and ground diameter for seedlings of different provenance. According to the seedling growth curves, the growth process of T. sinensis provenances can be divided into three stages. Rapid growth stage is the key time for seedling growth. During this stage the management of water and fertilizer should be reinforced to promote T. sinensis growth.