By dictionary it means – a substance required in relatively large amounts by living organisms for better growth and development
In gardening “living organisms” resemble to the plants.
Primary macro nutrients are the elements used in largest quantity by plants that are essential to growth and health. They are Carbon, Hydrogen, Oxygen, Nitrogen (N), Phosphorus (P), Potassium (K)
Plants extract Carbon, Hydrogen and Oxygen from air and water. For healthy foliage and harvest gardeners needs to understand N-P-K needs of plants.
Example : Rose need more Phosphorous then tomatoes and cucumber which need nitrogen as main nutrient.
In most of fertilizer they highlight N-P-K ratio clearly. See below the red highlighted ratio.
Secondary macro nutrients are Calcium (Ca), Sulphur (S), Magnesium (Mg), Silicon
Hope this article will help you to understand NPK jargon in gardening talks and give you understanding that plants do need nutrients to give you healthy harvest 🙂