Potatoes have a high requirement for potassium (K), which is the nutrient most absorbed by the crop. Previous studies have shown that potato cultivars can vary in their response to the source and form of potassium fertilizer applied. In Colorado, the major source of K fertilizer applied is potassium chloride (KCl) and potassium sulfate (K2SO4) as dry formulations, applied pre-plant. Potassium nitrate (KNO3) can be applied as a dry or liquid formulation. It provides readily soluble and quickly absorbed K in comparison to other sources of K fertilizer. These characteristics make KNO3 very effective for foliar applications during crop growth. A field study was conducted at Colorado State University’s San Luis Valley Research Center, with the objective of evaluating the effect of form, and timing of KNO3 fertilizer application on tuber performance of Canela Russet potato. Treatments included (i) a blend of K2SO4 and dry KNO3 applied pre-plant + side dress with dry KNO3 up to row closure (ii) Pre-plant application of K2SO4 + foliar application with liquid KNO3 up to row closure (iii) Pre-plant application of K2SO4 + spoon feeding liquid KNO3 during the growing season (iv) Pre-plant application of K2SO4 + alternate side dressing with liquid and dry KNO3 up to row closure (v) Pre-plant application of K2SO4 as control. Total K fertilizer applied for each treatment was 336 kg K/ha. Treatments (i), (ii), and (iv), enhanced tuber bulking, increased total and marketable tuber yield, and improved Agronomic K Use Efficiency. Data from this study indicate that side dressing or foliar application with KNO3 fertilizer up to row closure can improve tuber performance of Canela Russet potato in the field.