What the heck is N-P-K (npk fertilzer rating)?

Every package of fertilizer lists an N-P-K (NPK) rating on the label. What does it mean? It is the percentage of Nitrogen (N), the percentage of Phosporus(P) and of Potassium(K) found in that particular mixture of fertilizer. My hydroponics fertilizer shows "10-8-22" for an NPK rating meaning that by volume it contains 10% Nitrogen, 8% Phosphorus and 22% Potassium. Since this adds up to 40%, it means that the remaining 60% of the fertilizer is made of inert compounds.

It is really just a general guideline as to the potency of the fertilizer.

Don't take this rating too seriously because the same fertilizer in liquid form will have a lower overall NPK rating than it's exact counterpart in powder form due to the fact that in liquid it is a little more diluted by volume.

This rating is also misleading because it does not show any other nutrients at all.

For example, my favorite nutrient powder is 10-8-22 which seems rather low for a complete fertilizer when in fact it contains many other nutrients making it a complete fertilizer. Another fertilizer with the same NPK may lack the other nutrients and would not be able to be used alone.

So, when checking the quality of a fertilizer, use NPK as a very rough guideline - check the actual percentages of all nutrients listed on the back of the package.

If you like this website, consider downloading this free toolbar for your browser.

Previously I featured a conduit toolbar with radio for download but replaced it with the Alexa toolbar featuring website anaysis tools along with real-time related links to facilitate searching. Alexa is owned by Amazon and will not embed spyware into their toolbar. It's safe and it's free!

Download