Camellia formosensis (Masam. & Suzuki) M.H.Su, C.F.Hsieh & C.H.Tsou is a tree species with high economic value. During its vegetative phase, the top bud and two tender leaves are commercially harvested. This study investigates the reproductive phenology of C. formosensis in Shanping Forest Ecological Scientific Garden, Kaohsiung, Taiwan and analyzes the correlation between its phenological growth stages and environmental factors. A phenological survey of five C. formosensis trees was conducted weekly, from January 2019 through December 2023. Two primary reproductive phases (flowering and fruit development) and six secondary phenological growth stages, were identified and documented. To investigate the relationship between reproductive phenology and meteorological factors, Pearson correlation analysis was conducted to assess the correlation between the monthly mean number of open flowers and meteorological variables. To determine the optimal seed harvest period, each open flower was tagged with different colors and dates, and monitored weekly in 2019. A total of 20 fruits were collected at developmental intervals of 7, 8, 9, 10, 11, and 12 months from flowering to fruit maturation. The fresh weight, length, and width of each seed were measured, followed by measurement of cotyledon weight, length, and width after seed coat removal. The results revealed that the flowering peak of C. formosensis occurs from November to January, that is, during the dry season and at lower temperatures. Monthly mean temperature, minimum monthly temperature, monthly mean precipitation, and number of rainy days per month revealed a significant correlation with the monthly mean number of open flowers. Camellia formosensis seeds reached maturity after 11 months of development. Therefore, we suggest that the optimal period for harvesting C. formosensis fruits is from October to December.