NPK stands for the initials of the essential chemical elements that make up plant fertilisers.
N – Nitrogen
P – Phosphorous
K – Potassium
They are vital for healthy plant growth, but not always readily available in the soil. Some soils are deficient in one or more element and need some extra help, and certain plants require exceptionally high levels of an element.
To make the most of your plants, there’s a range of NPK fertilisers available with different ratios of each element. This means you can tailor the fertiliser to the specific needs of your garden, saving time and money.
The percentage levels of each element present in the fertiliser are indicated by three numbers, representing the N-P-K in that order.
For instance, a balanced fertiliser for general purpose usage will read 5-5-5, which is an equal 5% of each element. A high nitrogen fertiliser would be shown as 12-5-5, and high potassium would be 5-5-12.
Nitrogen is needed to produce leaves, stems and vegetation growth, so high nitrogen fertiliser is best for lawns and leafy vegetables. Plants lacking in nitrogen will have stunted growth, weak stems and yellowing or discoloured leaves from the tip inwards.
Phosphorus is essential for seed germination and for young plants to develop good root growth. Root vegetables such as swede, carrots and turnips need a high phosphorous fertiliser.
Plants deficient in phosphorous may have a purple tint to their green leaves and withered leaves that drop prematurely.
Potassium, sometimes referred to as potash, is essential for flower and fruit growth and also helps plants fight disease. For fruiting and flowering plants, look for a fertiliser with high potassium and low nitrogen levels. This will encourage fruit and flowers without promoting too much leaf growth.
If a plant has insufficient potassium levels, it will have poor flower production and low quality fruit and vegetables. It may also have curled or crinkled leaf edges with the appearance of dryness.
Before you buy any garden fertiliser, it’s worth checking what kind of plants you have and what needs feeding. Then just look for the right NPK plant fertiliser – the numbers will be clearly marked on the pack. Application will vary between types of fertiliser, so always read the pack before you start.