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Q.How To Calculate Soluable Fertilizer Dosage Per A Plant

Zone 21311 | Mladen added on June 8, 2020 | Answered

Let’s say I have a 15-15-15 water soluable fertilizer. It first needs to be saluted in water, and then given to the plants, right? Okay then, how much water should I use per say a table spoon of a fertilizer? And then when then solution is ready, how much should I provide it for each plant? Is there some generic way to calculate this for any fertilizer? I’m not asking only for an answer, but also for an explination, if I may. 🙂 And I’m asking for both liquid and powder water soluable fertilizers. I think it also doesn’t matter wether the fertilizer is organic or chemical, does it? If the NPK numbers are the same, and both are water soluable, then it could be just any fertilizer, right?

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Certified GKH Gardening Expert
Answered on June 10, 2020

Each manufacturer has different concentrations, so you will want to follow all application rates according to packaging.

Also, different plants require different NPK values, so it is best to match the fertilizers to the needs of each individual plant as closely as possible.

A carbon atom is a carbon atom, no matter where it comes from. This is true for most fertilizers. Each component is a compound that can be made, or extracted. The only real differences are purity.

Cheap manufacturing methods can leave you with unstable products, impurities, and residue from the synthesis process.

Pharmaceutical grade nutrients contain no impurities, are stable for long periods, and are most readily available to the plant immediately.

Obviously, with organic sources, Mother Nature creates the chemicals over time, and releases them in raw, usable form.

If I'm not creating my own soil through microbial means, I'm going to be using pharmaceutical grade plant food. That would be my preference outside of a proper organic soil.

Again, it is important to follow manufacturer instructions when feeding. They will have different mix ratios.

Here is an article for more interesting information on NPK values:


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