In this paper analyzed is the frequency of occurrence of the starting dates of the vegetation periods in the Lublin region in the specific time periods. The starting dates were determined using the Huculak and Makowiec method, in which values of mean daily air temperature were used. In the next step, the starting dates of the vegetation period were grouped in 5 dividing rows. The limits of the rows were determined using the standard deviation calculated for the investigated case (δ ≈ 12 days) and the mean starting date of the vegetation period (April 2).
It was stated that there was a high time changeability in the starting dates of the vegetation period, which was proven by the presence of cases in all the classes. The frequencies of occurrence of the particular types of starting dates, illustrated in the climate maps, indicate that the spatial differentiation of the dates is lower for the typical vegetation period starting date – same as in extreme cases described as abnormal. A higher differentiation was observed for the cases in the classes of early and late dates. In the Western part of the Lublin region it was stated that the frequency of the early season was higher. Moving towards North and Southeast, the frequency of late start dates of the vegetation periods increased. The analyzed 40-year series of data (according to the WMO regulations) is representative of the region and the elaborated classification can be the ground for the future comparison analysis of the last 15 years. The created classes can be a significant index in the assessment of the starting dates of the vegetation period in the Lublin region.