This study aimed to monitor meteorological parameters affecting the growth of Hashemi rice cultivar seedlings and grain yield in nursery conditions over two cropping seasons (2023-2024) in a complete randomized design with four repetitions and two treatments: Non plastic-covered nursery and plastic-covered nursery at the Gilan Agricultural Meteorology Research Center, Rasht, Iran. In each nursery, temperature sensors were installed to record the air temperature inside the nursery for 42 days from 4 April to the time of transplanting (15 May). The dimensions of the nursery were considered to be 2 meters wide and 8 meters length. The graphs of temperature sensors were replaced every week on Monday at 06:00 GMT (equivalent to 9:00 AM) according to the rules of the World Meteorological Organization (WMO) and a new graph was installed to record data for the following week. To measure soil temperature, a soil thermometer was installed inside the nurseries at a depth of 10 cm and soil temperature was recorded daily. In this experiment, minimum and maximum air temperature, soil temperature, sunshine hours, cloudiness, height, fresh and dry weight, grain yield, chlorophyll content and antioxidant enzyme activity were investigated. Regression analysis revealed that temperature was the most critical factor influencing germination and seedling growth. During the monitoring period, the external temperature fluctuation reached up to 35 °C with a soil temperature of 16 °C, whereas inside the plastic-covered nursery, temperature fluctuations occasionally reached 65 °C with a soil temperature of 18 °C. Comparison of the mean treatments showed that The highest seedling traits were observed in the nursery without plastic cover: height (38 cm), fresh weight (0.23 g), dry weight (0.04 g) and grain yield in the main field (2437.5 kg.ha-1) in the second year. In contrast, the plastic-covered nursery showed lower performance: height (28 cm), fresh weight (0.19 g), dry weight (0.02 g), grain yield (2054 kg.ha-1), chlorophyll content (23 SPAD), catalase enzyme activity (19.52 µmol g⁻¹ FW min⁻¹), superoxide dismutase enzyme activity (12.14 µmol g⁻¹ FW min⁻¹), and peroxidase enzyme activity (1.10 µmol g⁻¹ FW min⁻¹). Considering the same conditions in input consumption during the two cropping seasons, it seems that the minimum and maximum temperatures have shown a significant difference compared to the year 2023. Grain yield had a positive and significant correlation with seedling height (r2=0.92**), fresh weight (r2=0.94**), dry weight (r2=0.92**), chlorophyll content (r2=0.95**), catalase enzyme activity (r2=0.88**), superoxide dismutase enzyme activity (r2=0.90**), and peroxidase enzyme activity (r2=0.79**). In general, these results suggest that the range of temperature fluctuations in the plastic-covered nursery was significantly wider and included destructive temperature peaks. This intense temperature variation was statistically significant in the maximum temperature, while no severe fluctuation was observed between the two nurseries in the minimum temperature. In plastic-covered nursery, high temperature fluctuations caused heat stress and leading to reduced seedling vigor and yield potential in Hashemi rice cultivar. The controllability of the nursery environment under plastic cover can improve initial growth and seedling quality, but this advantage does not necessarily lead to improved final grain yield and can even reduce yield in some circumstances.