To study the impact of different potassium fertilization rates (0.0, 25, 50 and 75 kg K2O/ feddan), sowing dates (1st October, 15th October, 1st November and 15th November) and their combinations on growth and productivity of fennel plants, a field experiment was done at privet Farm in Taha El-Marg Village, Diarb Nigm District, Sharkia Governorate, Egypt during 2021/2022 and 2022/2023 seasons. The findings indicated that fennel plants that were fertilized with a rate of 75 kg K2O per feddan exhibited a substantial increase in plant height, number of branches per plant and total plant dry weight, in comparison to the other rates of potassium application. Moreover, the maximum values of yield components including umbels number per plant and fruit yield per plant and per feddan, volatile oil production including volatile oil percentage and fruit yield per plant and per feddan and total chlorophyll content and potassium percentage in leaves were produced with the same rate of potassium. In general, the most effective treatments in all assessed parameters of fennel were observed when the plants were sown on 15th October with significant differences with the other sowing dates under study. Fennel plants that were fertilized with either 75 or 50 kg K2O per feddan and sowed on 15th October exhibited the highest fruit and volatile oil yield per feddan. Notably, there were no significant differences seen between the two fertilization levels. Finally, the recommended treatment of this study was fertilized plants with 50 kg K2O/ feddan under 15th October sowing date under Sharkia Governorate conditions.