Potassium is the third primary nutrient contained in complete fertilizers. Plants use potassium to maintain their salt balance, and in many other ways. (For information about potassium deficiency in plants, see Potassium Deficiency.) All potassium fertilizers are mined from the ground, either as potassium sulfate or as potassium chloride. They can be bought in these forms, but are most commonly purchased as part of a complete fertilizer. Potassium is soluble, and usually remains in solution in the soil water, but it adheres to clay particles and humus in the soil, so it is not as readily leached from the soil as nitrogen. Potassium is about midway between nitrogen and phosphorus in persistence in the soil. In soils that are rich in clay or humus, one application a year is often enough. But in sandy soils or in containers, potassium should be applied more frequently. Eastern and southern soils, which receive abundant rainfall, are usually deficient in potassium, and need regular applications. Western soils usually need added potassium only for heavily cropped areas, such as vegetable gardens or annual beds, and on lawns and container plants.
Related Links
How to Read a Fertilizer Label
Minor Nutrients
Nitrogen
Phosphorus
Potassium Deficiency
