Here is some information:
http://www.answers.com/topic/potash
scroll down to US history encyclopedia:
here is an exerpt:
Potash (potassium carbonate) and soda (sodium carbonate) have been used from the dawn of history in bleaching textiles, making glass, and, from about A.D. 500, in making soap. Soda was principally obtained by leaching the ashes of sea plants, and potash from the ashes of land plants. In their uses, potash and soda were largely but not entirely interchangeable. Indeed, before the mid-eighteenth century, people only vaguely differentiated between the two.
With the advent of gunpowder at the end of the Middle Ages, potash found a new use for which soda could not substitute: the manufacture of saltpeter. Thus, the increasing demand for glass, soap, textiles, and gunpowder in sixteenth-and seventeenth-century Europe accelerated the decimation of the forests from which producers obtained potash. In 1608 the first settlers in Virginia established a "glass house," and the first cargo to Britain included potash. Britain obtained most of its potash from Russia, but a potash crisis in about 1750 led Parliament to remit the duty and led the Society of Arts of London to offer premiums for the production of potash in America.
Potash-making became a major industry in British North America. Great Britain was always the most important market. The American potash industry followed the woodsman's ax across the country. After about 1820, New York replaced New England as the most important source; by 1840 the center was in Ohio. Potash production was always a by-product industry, following from the need to clear land for agriculture.
By 1850, potash had gained popularity as a fertilizer, but forests available for indiscriminate burning were becoming ever scarcer.
