Potash is created from ash or lye* at an ashery by a dwarf with the potash making labor enabled. Potash has a value of 15 and does not have quality modifiers. Potash is used for fertilizer on farm plots. Fertilized farm plots have larger yields, as measured by the larger stacks of the plant when harvested. It can also be refined into pearlash.
- (*Yes, you could turn ash to lye and then that lye to potash, or just turn ash directly into potash - same end result, your choice.)