Actually, this should be titled "Potash Fertilizers" since potassium (K) is commonly available only as a part of the compound with oxygen called potash which has the chemical formula of K2O .

The way nutrients are absorbed by plants is when they are in water solution. So, the more soluble the nutrient, the easier it is to move it into the plant. However, solubility also means that the nutrient is likely to leach through the soil faster also. Of the three nutrients commonly found in commercial fertilizers, nitrogen is the most water soluble, followed by potassium (potash) with phosphorus (phosphate) being the least soluble.

Each year, a moderate percentage of the potassium applied will be used during that season. For this reason, it may build up over time. After several years of adding potassium to the soil, you may find that you do not have to use any for several years. Of course, you should periodically take a soil test to determine the exact levels in your soils.

Fertilizers - Every bag of fertilizer must contain 3 numbers that represent the percentages of the following nutrients: Nitrogen - Phosphorous - Potassium. So, the third number on a bag of 18-12-10 fertilizer shows that it contains 10% potassium in the form of potash.
  • Granular Fertilizers - All the typical bags of fertilizer that you find at the local garden center or hardware store contain potash. As soon as the granule dissolves in water, it becomes available to the plants.

  • Liquid Fertilizers - The standard liquid fertilizers used for container grown plants also contain the potassium in the form of potash.

  • Muriate of Potash - This is a single nutrient fertilizer with an analysis of 0-0-60 meaning that it is 60% potash. It may be handy when the soil test indicates only a need for potash and not for phosphorus.

  • Specialty Fertilizers - There are a number of special fertilizers that contain the primarily potash but they would rarely, if ever, be used in the home landscape. These would include potassium chloride, potassium sulfate, potassium magnesium sulfate, potassium hydroxide and potassium nitrate.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


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