It's got lots of uses . . . even as a laxative!
In growing, it's used in various strengths to fix potassium shortage, which shows as yellowing . . . however, there are many other plant issues that cause yellowing besides low potassium.
I've read on here 1TB per gallon, for K (potassium) deficiency.
I often add 1/4 tsp to a gallon when I water, just as a precaution. It's best to crush it up finer before putting it in water.