To investigate the effect of potassium source and rate on soil K, growth and K uptake of spinach, a pots experiment was carried out during the winter season of 2020 at the greenhouse of the Faculty of Agriculture, Saba Basha, Alexandria, Egypt. The experiment was laid out in randomized complete block design (RCBD) with three replications. The treatments included applying 50% of recommended K in the form of potassium sulfate (PS50), 100% as potassium sulfate (PS100), 50% as potassium citrate (PC50), 100% as potassium citrate (PC100), 50% as potassium humate (PH50), 100% as potassium humate (PH100) and control (0% K). The obtained results showed that the application of potassium in the forms of potassium humate and potassium citrate improved spinach growth and K uptake compared to potassium sulfate. The application of potassium humate can minimize the potassium application rate and reduce the fertilizer requirements without significant influences on plant growth and potassium uptake.