The Science Behind Fertilising

Simply put, fertiliser is required for soils that are lacking in nutrients that a plant needs to perform at its best.

You can tell if a plant needs feeding by some of the deficiency symptoms they display, we call this the science of fertilising, such as yellow leaves (lack of nitrogen), no flowers (lack of phosphorus), weak stems (lack of potassium) or localised necrosis, evident by stunted growth and possibly curling leaves (a lack of calcium).

The Science Behind Fertilising

The most common fertiliser ingredients include Nitrogen (N), which promotes vegetative growth and the greening of plants; Phosphorus (P), which is critical for root growth, and Potassium (K), which is essential for vigorous growth improving flower and fruit production. Plants also use several trace elements or micronutrients in small quantities, like boron, cobalt, copper, iodine, iron, molybdenum, manganese, selenium, zinc, silicon, nickel and chlorine. Some of these can be present in fertilisers, depending on the product and its intended use.

Nutrients can be recycled into the soil in natural ways, such as through decomposing leaves and plants. Soils can also be improved by crop rotation and planting green manures. It’s not always ideal to use fertilisers, and more fertiliser is not always better – a balance is essential. A plant only uses what it needs, and absorbing more than it requires can result in abnormal growth.

You may decide to fertilise a particular section of your garden before planting the next crop if you have grown and harvested plants there before and know that your soil will be depleted of nutrients.

As a general guide, and we do mean general as different climatic zones and different products make a difference in what you need for your particular garden, use 2:3:4 every 4 – 6 weeks year-round for good roots. These numbers refer to the percentage of nitrogen (2), phosphorus (3) and potassium (4) in the bags total weight. For leafy greens like spinach, use a fertiliser high in nitrogen (for leafy growth), like 7:1:3, every second month.

Feeding and fertilising tips

• Always water well after fertilising. In fact, donning a raincoat and fertilising in the rain is ideal!
• Always trust the manufacturer’s advice when deciding how much fertiliser to use per area – they are the experts, and adding more will not make it work any faster, plus it may damage your plants.