About Potassium in Fertilizers


Potassium is a common ingredient in fertilizers, usually found in potash, or potassium chloride, form. Plants absorb potassium from the ground in order to nourish themselves, and when there isn't enough natural potassium, they will begin to suffer. Potassium in fertilizers replaces the element in the soil, giving plants what they need to stay healthy.

Potassium Deficiency

  • Some plants will show visible signs of potassium deficiency, signaling their need for potassium fertilizer. The leaves of grain plants will begin to look burned or scorched, while alfalfa leaves will be affected by yellowish spots. Look to the lower leaves of plants first for signs of potassium deficiency.

Applying Potassium

  • Adding potassium fertilizer at the time of seeding is one of the best ways to provide potassium to new plants, but too much potassium may result in delayed growth. If soil is extremely lacking in potassium, broadcasting fertilizer by hand over a large area is the most effective way of providing this needed element. Gardeners commonly apply fertilizer to soil in spring and fall. Always thoroughly moisten soil after applying fertilizer.

Chemical Makeup

  • Potassium chloride (KCl) is the most commonly used potassium in fertilizer. Commercial fertilizers may also contain potassium sulfate, also known as sulfate of potash, which is used on tobacco and vegetable crops. Potassium magnesium sulfate, also called sulfate of potash magnesia, is also blended into fertilizer form to provide magnesium. Caustic potash, or potassium hydroxide, is found in liquid mixed fertilizers.


  • Nitrogen, phosphorus and potassium are the most commonly used elements in commercial fertilizers, as plants absorb these from soil more quickly than other nutrients. Commercial fertilizers are labeled with a series of three numbers to indicate the amount of nitrogen, phosphorus and potassium, in that order, the mixture contains. Each number represents a percentage weight. For example, a 10-30-10 mix indicates 10 percent nitrogen, 30 percent phosphorus and 10 percent potassium. In fertilizer, potassium is often indicated by K2O, the chemical formula of potash.

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