Lawn Fertiliser Labels: NPK
These may look tricky to begin with but it is really quite simple.
There are normally three numbers on a fertiliser label that describe the nutrient content of the bag e.g. 18-3-8. The first number is the nitrogen (N) content. The second is the phosphate or phosphorous (P) content and the last is the potassium (K) content. Hence people talk about the NPK values of fertiliser.
Each number is expressed as a percentage. So the various contents are:
18 grams in 100 grams of fertiliser is nitrogen
Phosphate is 3%
3 grams in 100 grams of fertiliser is phosphorous
Potassium is 8%
8 grams in 100 grams of fertiliser is potassium
If you add this up you get 29% or 29 grams of nutrient in 100 grams of fertiliser. So what’s in the rest of the bag?
Well, your nitrogen content is not just nitrogen because that’s a gas! It is in the form of a chemical compound usually a salt like urea, perhaps with a slow release coating. Some fine granular fertilisers also contain an organic base to improve the soil. This all adds up to give you your 100% or 100 grams.
Manufacturers, including Lawnsmith make up lawn fertilisers in a variety of nutrient combinations for many different types of turf and times of year. This makes it very confusing and difficult for the homeowner to know what and when to apply to their grass which is why, where possible, we give our fertilisers simple names like Spring & Summer or Autumn. Hopefully all will become clear as you progress to the next few pages.