Blooming phenology and pollen production in the five Oenothera species were investigated during the period of 2013–2015 in the Lublin area, SE Poland. The blooming period was relatively long, and flowering usually started in the middle or late June and lasted until late July or the middle of August. The Oenothera species studied exhibited nocturnal anthesis, i.e., the flowers opened in the late evening and lasted overnight until the early morning hours. Plants developed a great number of flowers per individual and per unit area (on average, 158 and 4,136, respectively), and this feature appeared to be species-specific. It was demonstrated that the blooming phase had an impact on the mass of anthers and pollen produced per flower in all Oenothera species. In general, the greatest mass of anthers and pollen was observed at the beginning of blooming, and with the progress of flowering, the values decreased. However, statistical differences were found for O. flaemingina, O. paradoxa, and O. rubricaulis. The mass of pollen produced per unit area was also a species-specific characteristic and was related to the abundance of flowering. The greatest amount of pollen was produced by O. flaemingina (30.6 g m−2), which was almost three times more than that produced by O. rubricaulis (10.9 g m−2). The protein content of pollen grains was relatively low and on average amounted to 15.4%. The Oenothera species examined in this work may be considered valuable pollen yielding plants. Nevertheless, given the invasive potential of species from subsect. Oenothera, precautions are suggested during cultivation and/or planting these taxa in bee pastures, in order to prevent uncontrolled spread into new areas.