NPK - All fertilisers contain at least one of the major plant foods - that is:

  • Potash (Potassium Oxide) - (K) - for flower and fruit production

  • Nitrogen (Nitrate) - (N) - for stem and leaf growth;
  • Phosphate (Phosphorus Pentoxide) - (P) - for root growth



Plants also need small amounts of "trace elements" such as iron, magnesium, boron and manganese. Some fertilisers contain these as well.

Straight fertilisers supply only one major plant food.

Compound fertilisers supply at least two major plant foods.

Balanced or General fertilisers supply all three but not necessarily all in the same proportions.


Fertilisers can be either organic (derived from animal or plant remains) or inorganic (mined from the earth or man-made). Inorganic fertilisers are usually quicker acting. Fertilisers come in different forms, powder or granular for spreading on the soil and raking or hoeing in and as liquids or soluble crystals for applying with the watering can.


All proprietary brands of fertiliser, whether in bags or bottles, should display the analysis, or the N:P:K ratio. For example, if the N:P:K ratio is 7:7:7, as in Growmore, you know that the fertiliser contains equal proportions of the three major plant foods, nitrogen, phosphate and potash and is, therefore, suitable for general use with all plants.


Every plant requires all three major plant foods, but at different stages of growth they are needed in different proportions. For example a flowering or fruiting plant, which includes many vegetable crops, requires some phosphate in the early stages, to promote root growth, followed by a fertiliser high in nitrogen for the growth stage and then one which is higher in potash to ripen the plant and assist in flowering and fruiting.


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