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, 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 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,…
