It is stated, that air temperature is the leading element of the climate, including its changes, of which a well-known indicator of these changes is the seasonal dynamics of plant pollen occurrence, on the local and regional scales. The aim of this study was to assess the variability of pollen seasons in Poland in terms of temporal and spatial aspects and potential trends in seasonal dynamics related to air temperature. The pollen seasons of five allergenic plants (alder, hazel, birch, grass, and mugwort) at eight sites in Poland from to 2001–2020 were analysed. The seasonal parameters were assessed against the thermal conditions, that is, the mean monthly values of air temperature (in °C). To determine the trends in air temperature changes, measurements over a longer period (1961–2020) and a linear regression equation were used. The beginning of the pollen seasons in Poland is highly variable for early pollinating trees is closely related to the ongoing rise in air temperature during winter months, mainly in December. Birch pollen appeared earlier in Poland because of the increasing trend in the average monthly air temperature in April. Warm and humid summers contribute to a higher SPIn value for grass pollen, whereas warm and dry summers do not affect the season intensity. The mugwort pollen seasons are getting shorter due to lower temperatures in June and July. The present study showed a clear increase in the mean annual air temperature in all studied cities, which affected the pollen season of allergenic plants.