The relationship between weather conditions and the onset of the flowering and ripening stages of winter rapeseed was studied based on meteorological data and field observations from the Experimental Stations for Cultivar Testing (COBORU) in Bezek near Chelm in the period from 1974/75 to 2008/09. The Pearson’s correlation and linear regression analysis were used in order to determine the correlation between meteorological elements and dates of onset of the two stages. The study showed that the onset of flowering and ripening was strongly associated with thermal conditions in April and May. The relationship between growth and development of winter oilseed rape in the period from March to July and the values of air and soil temperatures in winter was also noted. Later dates of the onset of flowering and ripening were influenced by greater number of days with ground frost and decrease in sunshine duration in spring. There were no statistically significant correlations with precipitation and Ped’s drought index. Furthermore, in recent years, the occurrence of early dates of onset of the two stages was found. In the case of the onset of flowering, a statistically significant (α = 0.01) downward trend in the analysed area was indicated. It is probably associated with an increase of air temperature during the last two decades in Poland (from February to May).