JoeReal

One approach is to water with a premixed solution. The rule of thumb that I use is patterned after UCR's fertigation where each macronutrient do not exceed 300 ppm in the water. Just for the K (18%), you can mix about 1.2 teaspoon KMag to a gallon of water. Or dissolve 6.3 grams per gallon of water. This is the concentration that will not burn the roots of your plants every time you water. So you can water as much as your plant would need without worrying about over application. The excess will drain out, but water only just enough to minimize waste of nutrients. You can also mix proportionate amount of N, so that you achieve a 3-1-5 ratio.