Poppy cultivation has a long tradition in Central Europe. Growing winter poppy instead of the commonly grown spring poppy might increase seed yield, especially in the face of changing climatic conditions. However, knowledge regarding optimum sowing date and optimum sowing rate for winter poppy under Pannonian climate conditions in Central Europe is missing. Therefore, a two-year field experiment was performed in Eastern Austria with four sowing dates ranging from early September to mid/end of October and two sowing rates with 50 or 100 mg seeds m−2. Seed yields were considerably higher than values reported for spring poppy throughout all sowing dates, mainly due to a higher number of seeds capsule−1 and, thereby, a higher seed yield capsule−1. The highest seed yields were obtained by sowing in early October, while the earliest and especially the latest sowing date resulted in lower seed yields. Consequently, the optimum sowing date for winter poppy under Pannonian climate conditions in Central Europe is early October but sowing can be performed over a wider range of dates. No seed yield differences were observed between sowing rates. Consequently, the sowing rate can be much lower than the recommended sowing rate for spring poppy.