Understanding Fertilisers

All plants require nutrients for their growth and other functions. Fertilisers are applied to the soil to increase fertility so that the plants can grow vigorously and reproduce.

Get to know the different type of fertilisers, their advantages and disadvantages and when to apply them in your home garden.

Macro and Micronutrients

Macronutrients and micronutrients are essential for plant growth. Macronutrients such as Nitrogen (N), Phosphorus (P) and Potassium (K) are required by the plant in relatively large amounts while micronutrients like Iron (Fe), Copper (Cu), Zinc (Zn), Boron (B), Molybdenum (Mo) and Manganese (Mn) are needed in smaller amounts.

Nitrogen	Promotes growth of leaves of the plant
Phosphorus	Promotes the formation of lateral and fibrous roots Promotes flowering Increases the strength of plant stems
Potassium	Promotes formation and enlargement of fruits Increases disease resistance

If such nutrients are not adequate, adding fertilisers in the soil or growing media will help the plants to obtain them.

Types of Fertilisers

Fertilisers are classified as complete and incomplete and usually distinguished by the series of three numbers on the labels on their packs, like 14-14-14 or 16-20-0. These three numbers represent the value of the Nitrogen (N), Phosphorus (P) and Potassium (K) ratio of each pack, in which the higher the number the more concentration of nutrients in the fertiliser.

Complete fertiliser 1

Complete fertiliser contains these three primary nutrients of NPK and usually comes in the form of granules or pellets. Incomplete fertilisers supply only one or two of the primary nutrients and is available often in the form of soluble crystals.

How to Identify Fertilisers?

Organic fertilisers come from only plant or animal products or by-products such as chicken manures, leaves and compost. Generally, most organic fertiliser will be darker coloured and in the form of powders, granules or of uneven texture.

Inorganic or synthetic fertilisers are produced artificially and come from sources other than animals or plants. They usually contain mineral and chemical products. Since they are manufactured, they are available in various forms such as granular white crystalline, granular colourless or coloured crystalline.

Advantages and Disadvantages

Organic fertiliser Advantages Disadvantages
Release nutrients gradually (Prevents over fertilisation which is harmful to plants)

Improves the structure of the soil and increases its ability to hold water and nutrients

Little to no risk of toxic build-ups of chemicals and salts that can harm the plants

Renewable, biodegradable, sustainable, and environmentally friendly

Nutrient ratios are often unknown, and the overall nutrient percentage is lower than chemical fertilisers

May attract pests and diseases

It takes time for the nutrients to be supplied to the plants and improvements to the plant may take more time

Inorganic fertiliser Advantages Disadvantages
Nutrients are available to the plants immediately and improvements can occur in days

Highly analysed to produce the exact ratio of nutrients desired

Standardised labelling makes ratios and chemical sources easy to understand

Relatively inexpensive

Chemical fertilisers are made from non-renewable resources such as fossil fuels

They help plants grow but do nothing to improve soil structure

Chance of over fertilisation if used wrongly. This can not only kill the plants but upset the entire ecosystem.

Chemical fertilisers tend to leach or filter away from the plants, requiring additional applications.

Toxic build-up of chemicals and salt

Before you apply fertiliser, you should have your soil tested to determine what type of fertiliser your soil needs. Your plants may also show visual clues (symptoms) that aid in determining the nutrient deficiency.

Common Symptoms of Nutrient Deficiency

Nitrogen (N)	Phosphorus (P)	Potassium (K)
Leaves turn pale yellow (chlorotic) Poor, stunted growth	Stems, petioles and underside of leaves turn purple, orange or red. Occur first in lower leaves	Tips of older leaves turn brown, or the plant has a burnt appearance on leaf tips and margins
Magnesium (Mg)	Iron (Fe)	Boron (B)
Paleness between veins on older leaves. As symptoms progress, leaves shrivel and die	Yellowing (Chlorosis) between veins on younger leaves	Tips of leaves become hook in appearance

Learning More

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Text from Plant Science and Health Branch

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Understanding Fertilisers

National Parks Board