NPK is the abbreviation for the three most important plant nutrients: N stands for Nitrogen, P for Phosphorus, and K for Potassium. They are called macronutrients because the plant needs them in relatively large quantities. Almost every fertilizer indicates its ratio of these three elements as an NPK number on the label.
The three main nutrients
Nitrogen (N) is the engine of leaf growth and is especially crucial during the vegetative phase. Phosphorus (P) supports roots and flower formation and becomes more important during the flowering phase. Potassium (K) strengthens overall resistance, water balance, and flower development. In addition to NPK, there are secondary and micronutrients such as calcium, magnesium, or iron – which the plant needs in smaller quantities, but they are still necessary.
Reading NPK on the label
On fertilizers, the NPK ratio is usually presented as three numbers, for example, "7-4-10". They indicate the proportion of nitrogen, phosphorus, and potassium. Growth fertilizers typically have more nitrogen, while bloom fertilizers have more phosphorus and potassium. The best way to control how much you give is by monitoring the EC value – and keeping an eye on over-fertilization.
Frequent questions about NPK
What do the three letters stand for?
For Nitrogen (N), Phosphorus (P), and Potassium (K) – the three main plant nutrients.
Which nutrient is important during flowering?
Mainly phosphorus and potassium. Nitrogen demand decreases compared to the growth phase.
Is NPK alone sufficient?
No. Additionally, the plant needs secondary and micronutrients such as calcium, magnesium, and iron – just in smaller quantities.
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EC value
Overfertilization