<p>This study evaluated the effect of potassium enrichment in the nutrient solution (NS) on the growth and yield of two <i>Capsicum</i> cultivars (cv. Bachata and Red Jet) under a partially controlled greenhouse environment.&#xa0;Various potassium (K⁺) treatments (0, 280, 317 and 420 mg L^− 1) were applied to assess their impact on growth attributes, nutrient uptake, ionic traits, gaseous exchange, antioxidant defenses and yield. The results indicating that plants grown without K⁺ application exhibited a marked reduction in studied parameters. In comparison to control, potassium treated plants (317 mg L^− 1) showed significant improvements in shoot length (1.54&#xa0;cm), root length (1.86&#xa0;cm), stomatal conductance (1.81 mmol H₂O m^− 2 s^− 1), leaf photosynthetic rate (2.51 µmol CO₂ m^− 2 s^− 1), and carboxylation efficiency (1.54&#xa0;mol m^− 2 s^− 1 bar ^− 1) along with higher potassium content (1.62%). soluble solid content (1.48 <b>°</b>Brix), phenolic compounds [1.84&#xa0;mg gallic acid equivalent (GAE) 100&#xa0;g^− 1], ascorbic acid (1.56&#xa0;mg 100&#xa0;g^− 1) and antioxidant enzyme activities including catalase (1.36 U mg^− 1 protein), peroxidase (1.37 U mg^− 1 protein) and superoxide dismutase (1.91 U mg^− 1 protein) were also enhanced, leading to a 3.05- fold increase in fruit yield. The Red Jet cultivar showed more pronounced improvements compared to Bachata.&#xa0;Therefore, the present study supports potassium enrichment (317 mg L^− 1) in nutrient solution and cultivation of Red Jet cultivar under partially controlled soilless greenhouse.</p>