Plants need potassium for metabolic processes. Photosynthesis, protein synthesis and enzyme activation needed for plant growth and reproduction could not occur without potassium. Potassium affects many attributes of a plant, including taste, size and shape.
Potassium also regulates water and the opening and closing of the plants stomata. Root development and yield of fruits and nuts are affected by potassium deficiency. Some common signs of potassium deficiency in plants include yellowing in between leaf veins, curling or brown leaves, or purple spots on the underside of plant leaves. Some plants, such as tomatoes and potatoes, have blue-green colored leaves as a result of potassium deficiency.