A research study was conducted to identify the effect of potassium rate and drought stress on the post-harvest soil potassium content and growth parameters of cowpea (Vigna unguiculata L.). The experiment was arranged in a Completely Randomized Design (CRD) in a factorial manner with 8 treatments (4 different rates of fertilizer potassium as muriate of potash (MOP (i) 100% of recommended level (75 kgha-1), (ii) 125% of recommended level (93.75.kgha-1), (iii) 150% of recommended level (112.5 kgha-1), and (iv) 175% of recommended level (131.25.kgha-1) at 2 different soil moisture conditions as 25% depletion and 75% depletion of available soil moisture as optimal and sub-optimal moisture condition respectively and was replicated 3 times. The post-harvest soil potassium content, chlorophyll content of leaves and cowpea growth parameters such as, dry weight of root and dry weight of shoot were recorded at vegetative and harvesting stages. The results reveal that there was a significant influence (p<0.05) of potassium rate and soil moisture on the growth parameters, leaf chlorophyll content and available soil potassium content after harvest. In overall terms potassium promoted growth of cowpea when subject to sub-optimal soil moisture. Further, it was found that the increased application of potassium fertilizer up to 175% of recommended level can be considered as a significant factor in overcoming soil moisture stress in cowpea.