Boiling hardwood ash in water creates runoff that can be processed to form either lye or potash. Potash contains high amounts of essential plant nutrients; therefore it is mostly used as an agricultural fertilizer. With a long history of mining and manufacturing, the potassium salts help form soap, glass, and dyes.

Chemically, potash consists of potassium carbonate, but also might contain potassium oxide or potassium chloride, depending on how pure you consider the mixture. Usually, potash takes the form of powdery salts. Modern methods of extraction almost all rely upon deposits mined from ores, like sylvanite.

Historically, the manufacture and trade of potash traces an interesting period in the New World's economy. As one of the largest cash crops of the late 1700s and early 1800s, potash established strong trade routes through upstate New York, Canadian provinces, and overseas to Russia and England. At a time when land covered in hardwood forests was more valuable as farmland, settlers felled hundreds of thousands of acres of trees. Not only did this create lumber for building, but also they found a way to extract even more money by creating potash.

The word potash is a compound of "pot" and "ash," showing how the salts were first made. All leftover tree material, including damaged branches and roots, were burned on a dry day. The most popular wood came from broadleaved trees, namely Elm.

When these ashes were soaked in hot water for a while, then filtered, the rudimentary stage of potash created lye. If this lye, filling huge pots in a kiln, was baked down to evaporate all the water, "black ash" resulted. Black ash was like an unfiltered kind of potash. Farmers could make far more money trading potash than either lumber or food crops.

Nowadays, our potash comes from mining and goes toward inorganic fertilizer rich in potassium. In fact, the widespread use of these kinds of fertilizers on major crops like corn, wheat, and vegetables means arable land yields more edible food per acre. Potassium protects plants against disease and pests, allows them to flexibly adjust to changing weather conditions, and encourages them to absorb more nutrients. The resulting crops are larger and more nutritious.