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Making a Fertilizer Concentrate

If you follow my recommendation of applying frequent, but very low concentration of fertilizer solutions, you may run into issues measuring “fractions of teaspoons” of your fertilizer for mixing. For example, if you want a 25 ppm N solution, you can use the simple equation of 2/%N to determine the teaspoons-per-gallon to mix. However, using K-Lite as an example, a 12.9% N formula, that would give us 2/12.9=0.155 teaspoons. How do we measure that? A 1/8 teaspoon measure is 0.125 and 1/4 teaspoon is 0.250. So…

Let’s make a concentrate and dispense that!

We just have to pick a convenient volume to dispense and make up a concentrated solution that can be added to a gallon of water to make up the proper, final concentration.

Let’s use a shot glass (1.5 ounce) as our dosage (convenient and handy), for example. A gallon is 128 ounces, so there are 128/1.5=85.333 shot glasses in a gallon. As each shot glass must contain 0.155 teaspoons, our gallon of concentrate must therefore contain 85.333 x 0.155 = 13.23 teaspoons of powder (13 is close enough). Breaking it down for easier measurement, 13 teaspoons is one quarter cup plus 1 teaspoon, so add that to a gallon jug, add water to reach one gallon in total volume, shake it up and you’re set to go! Store that gallon at room temperature, and each time you want to feed your plants, just shake it up and pour a shot-glass full in a gallon of water.

To save you from having to do that calculation, or if you wish to use a different concentration and/or dispensing volume, here we have a…