What is NPK?

What does NPK stand for?

N, P & K are the chemical symbols for nitrogen, phosphorus and potassium respectively. These are the three main nutrients required by a plant to grow and thrive. The NPK of a fertiliser is usually written as three numbers which refer to the percentage of that nutrient in the product. (The order of the numbers is important and if there is none of a particular nutrient it is generally left as a “0” rather than being omitted entirely.)

For example: 19-3-9, 6-5-10 or 8-0-6

In the UK the levels in the NPK description refer to the oxide forms of those nutrients, even if these forms are not actually present in the product itself. These are nitrogen (N), phosphorus pentoxide (P2O5) and potassium oxide (K2O). If you do want to know the elements levels though you can just check the “typical analysis” on the label as they are required to be included there by law (see below).

DroughtSafe Label

What about the other nutrients?

Fertilisers usually include other important plant nutrients such as Magnesium, Sulphur or Iron. When these are present they are usually added on to the end of the NPK in their oxide form like this…

22-5-10 +2.5%MgO +2.5%CaO

6-5-10 +6%Fe

How do I interpret the NPK of a product?

The levels of NPK in fertiliser change depending on what you want to use the fertiliser for. Spring/summer fertilisers tend to have a higher nitrogen content (e.g. 22-5-10, 19-3-9) whereas autumn/winter fertilisers tend to have higher potassium content (e.g. 6-5-10). Phosphorus is important for growth too so you’ll see a low level in most fertilisers, but when it is needed for seedlings or turf establishment we see it in higher levels (e.g. 6-10-8).

All of the GreenBest sales staff are able to advise on fertiliser use and can help you understand the products you are using. Call us now for a quick chat and let us help you understand your fertiliser! 01963 364788

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