Potash is the only source of potassium fertilizer; there are no practical substitutes. Potash helps improve a plant's disease resistance and crop quality, and increases yields.

The word potash is derived from the "pot ash" residue that resulted after evaporation during the process to yield potassium carbonate through extracting minerals from wood ash. The modern take of the word "potash" refers to any variety of salt that contains water-soluable potassium.

The latest news involving potash is the acquisition of Potash Corp of Saskatchewan by Australian mining giant BHP Billiton. If the deals go through, a single company will control more than 50% of the world’s potassium fertilizer productions, which may have important ramifications for world potassium fertilizer and thus food costs.