Depends on why you are using it and the brand/form you have. It isn't commonly used.

Dave

In pots, I would advise using no more than 5 g./gal. (about 1 tsp./gal.) for occasional feeding or 1 g./gal. water for feeding every time you water. In the outdoors ground, use 3X that concentration, because it will be diluted by rain. It is okay to fertilize with potassium nitrate before planting seeds because there is ample scientific evidence that it helps germination (Google it). Otherwise, like all fertilizers, it is best to titrate the dosage according to the established rate of growth.