The N-P-K Values

Every fertiliser you buy shows three numbers, be it 20-20-20, 15-30-15, or some other value. But what do these numbers represent? They show the percentage values of Nitrogen (N), Phosphorus (P), and Potassium (K) present in the plant food mix.

Nitrogen is the chemical whichs helps the 'green' part of a plant, which is why grass fertiliser (e.g. 24-4-10, 15-2-3) and evergreen tree food (e.g. 10-5-5) have such high first numbers, compared to the rest. Nitrogen also encourages the 'branching out' of plants.

Phosphorus promotes root growth, and strengthens the stems of the plant. This is why we recommend using Plant Starter (10-52-10) when transplanting, or growing from cuttings. At blooming time, it also helps give larger and longer-lasting blooms. This is why the likes of Mircle-Gro All-Purpose and Geranium and Bedding Plant Food (both 15-30-15) help produce impressive blooms.

Potassium provides overall strength to the plant, helping to prevent against disease and insects. It also improves the formation of fruit and vegetables, due to its aid in the plant's formation and storage of sugars and starches. You can see the logic behind the Vegetable Booster (10-14-21) ratio, and Tomato Food (6-12-12) composition.