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All about NPK Fertilisers

Sep 14,2021 | Cassandra Low

Have you been wondering why your plants are not growing well? Having only sunlight, water, air and the right temperature alone is not enough for plants to flourish. Instead, applying fertilisers to the soil will help to make your plants grow and thrive. 


Credit: The Plant Rescuer 

Credit: The Plant Rescuer 

What are Fertilisers?

Fertilisers play an important role for soil health. They supplement natural supply of soil nutrients and help to build up soil fertility. Plants need 14 essential nutrients for their growth and health, which fertilizers provide. These nutrients are: nitrogen (N), phosphorus (P), potassium (K), sulphur (S), magnesium (Mg), calcium (Ca), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), nickel (Ni). Additional elements may be essential to a few plant species, e.g. sodium (Na) and cobalt (Co). 

Credit: Hort Americas 

When and how often do you use fertilisers? 

Fertilizer is most effective when used on plants at their peak growing cycle. Frequency of using fertilisers depends on the type of fertilisers. Usually, different fertilisers will have different specifications and directions for use. In general, soluble fertilizers are applied every two weeks during the growing season. Whereas, slow-release fertilizers work for months, thus one application is generally sufficient for the growing season.

Types of Fertilisers 

Fertilizer supplies plants with three primary nutrients: nitrogen (N), phosphorus (P), and potassium (K). This set of nutrient values is so important that it can be found on every fertiliser packaging. 

Understanding the N-P-K Values 

The NPK value represents the percentage by volume of nitrogen (N), phosphorus (P), and potassium (K) that a fertilizer contains. For example, a fertilizer with an NPK value of 24-8-16 would mean that it contains 24% nitrogen, 8% phosphorus, 16% potassium and the remaining containing filler ingredients. 

Nitrogen (N)

Nitrogen is needed for vegetative growth and production of lush foliage.

Symptoms of deficiency: Leaves turn pale yellow; plants have poor or stunted growth.

Phosphorus (P)

Phosphorus is used for the formation of lateral and fibrous roots, promotion of flowering and helps to increase plant stem strength.

Symptoms of deficiency: Underside of leaves turns reddish brown or purplish.

Potassium (K)

Potassium is used for fruit formation and enlargement. It also enhances resistance against diseases in plants.

Symptoms of deficiency: Leaves may have brown or yellow scorching at their edges and tips.

General fertilisers tend to have balanced NPK values (NPK 8-8-8, NPK 15-15-15), while specialized fertilisers will have a higher value of a specific macronutrient when a plant demands a higher or lower amount of one of the three nutrients. 

It is important to understand what your plants need as these NPK values will play a crucial part in ensuring healthy soil so that plants will be well grown.