NPK – what's it all about ?
You have surely seen the letters NPK written on packaging or in specialist magazines, but do you know what they mean?
NPK, the basic nutritive elements
NPK fertilizers contain the three main nutritive elements needed by plants during their development stage. These elements are drawn from the substratum. They will be used up quicker in a pot or in a window box than in a garden, so they will need to be replaced regularly.
- N stands for nitrogen, an element which helps the vegetative development of all parts of the plant above the ground. It is beneficial when planting, in Spring, when vegetation begins, and for leafed vegetables. However it should be carefully dosed as too much of it may hinder the development of flowers, fruit and bulbs. It can be found in dried blood, cut grass and in nettle slurry.
- P stands for phosphorus, a nutritive element which strengthens resistance in plants and helps root development. It can be found in bone powder and in bird droppings.
- K stands for potassium, an element which contributes to blossoming and fruit development. It can be found in wood ash.
The letters NPK are followed by three figures on fertilizer packages which correspond to the proportion of each of these elements in the product. For example a tomato fertilizer NPK 12.10.20 contains 120 grammes of nitrogen per kilo.
Examples of NPK proportions for specific fertilizers:
- Fertilizer for citrus fruit: NPK 14.4.28
- Fertilizer for lawns: NPK 20.10.10
- Fertilizer for geraniums: NPK 4.6.8
- Fertilizer for fruit trees: NPK 5.4.8
Other elements
Other so-called ''secondary'' elements are also essential for proper plant development such as calcium (Ca), sulphor (S), or magnesium (Mg). Less of these are needed and often there is enough of these in the soil.
Trace elements also play a determining part in plant development, contributing to the formation of chlorophyll and to healthy growth.