Two experimental fields were conducted during the two consecutive summer seasons of 2018 and 2019 at the Experimental Farm of Fac. Agric., Zagazig Univ., Egypt, to study the effect of potassium fertilization levels (0.0, 24, 48 and 72 kg K2O/feddan), ascorbic acid concentrations (0.0, 150 and 300 ppm as foliar spray) and their interaction treatments on vegetative growth parameters, yield components and chemical constituents in calyxes of roselle plants. The obtained results indicated that the highest level of potassium fertilization (72 kg K2O/feddan) gave the highest values of plant height and branch number per plant and total dry weight per plant compared to the other two levels and control. In addition, the yield components of roselle plants (number of fruits per plant as well as sepals and seed yield per plant and per feddan) and chemical constituents (total chlorophyll content in leaves, anthocyanin content, total soluble solids, nitrogen, phosphorus and potassium percentages in calyxes). Moreover, foliar spray with 150 and 300 ppm of ascorbic acid recorded the highest values of abovementioned parameters with significant difference between them compared to control (unsprayed plants). In conclusion, it could recommend that 72 kg K2O/feddan level interacted with 300 ppm ascorbic acid, reveals a uniform effect in enhancing of growth and yielding of roselle plants compared to the other interaction treatments under study.