Understanding NPK Ratio for Plant Fertiliser Labels

Understanding NPK Ratio on Plant Fertiliser Labels – We go through what these ratios mean for Nitrogen, Potassium and Phosphorous and how they affect plants.

When attending a garden centre in the hopes of finding some good fertiliser for your beloved plants, you may notice a NPK ratio labelled on the packet. So what use are they and what value do they have when it comes to gardening?

What does NPK stand for on fertiliser labels?

  • (N) Nitrogen
  • (P) Phosphorus
  • (K) Potassium

Each element is referred to as a macro nutrient and also refers to the amount of each nutrient in the fertiliser. Most nutrients for plants are provided in the soil, however due to differences in soil (nutrient amounts, soil type and pH level) – your plants may need a little extra attention with the help of fertiliser.

(N) Nitrogen

Nitrogen is responsible for leafy growth and is a key component in chloropyll which is responsible for photosynthesis (the process that plants use to convert the sun’s energy into food).

  • It helps the plant to grow quickly and also increases the production of seeds and fruit
  • Improves the quality of the leaf

What fertiliser contains a high concentration of Nitrogen?

  • Blood meal
  • Fish meal
  • Various liquid fertilisers such as Nitro Big

Nitrogen deficiency occurs when the plant is not obtaining enough Nitrogen. This can be recognised by the yellowing of the leaves or slow/stopping of growth.

(P) Phosphorus

Phosphorus is responsible for plant reproduction and is a key component in improving flowering, seed and fruit production.

  • It helps develop a strong root system
  • It is an essential part of photosynthesis

What fertiliser contains a high concentration of Phosphorus?

  • Rock phosphate
  • Bone meal
  • Various liquid organic fertilisers such as Neptune’s Harvest Fish & Seaweed

Phosphorus deficiency occurs when the leaves turn purple, the plant will have retarded growth and the fruit and flowers are poor.

(K) Potassium

Potassium is responsible for a wide range of physiological processes.

  • It helps maintain the plant and water balance
  • It helps in building the protein, photosynthesis, fruit quality and preventing disease
  • It helps to increase the strength for survival in Winter
  • Improves stem rigidity

What fertiliser contains a high concentration of Potassium?

  • Sul-po-mag
  • Greensand
  • Various liquid fertilizers such as Earth Juice’s Meta-K

Potassium deficiency occurs when there is reduced plant growth and yellowing and/or burning of leaf edges.