Outdoors ya but i dont count on it as being my standalone nutrient.... Its mixed into the hole along with alot of other things. Only pure ash thats white from a tree. Not a 2x4 or fence boards. I usually add ash into my compost bin to enrich the compost.
"Fertilizer potassium is sometimes called “potash”, a term that comes from an early production technique where potassium was leached from wood ashes and concentrated by evaporating the leachate in large iron pots (“pot-ash”)."
Fertilizer potassium is sometimes called potash. Potassium is removed from the soil in harvested crops and must be replaced to support future crop growth.