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NPK - Understanding your fertiliser
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What does NPK stand for?
When you see a bag of fertiliser, you often see the letters NPK on them and some numbers by or below them. This information is so customers can compare products. These three numbers form the fertiliser's N-P-K ratio. This simply is the percentage of three plant nutrients in order: Nitrogen (N), Phosphorus (P) and Potassium (K), it reflects each nutrient's percentage by weight.
For example, a 10 kg bag of Lawn Fertiliser with NPK 30-0-4 reveals that it contains 30 percent Nitrogen, 0 percent Phosphorus and 4 percent Potassium, in addition to its other beneficial ingredients. By multiplying 10kg by .30, you'll see that this 10 kg bag contains 3kg of actual nitrogen.
Why these three?
There are 17 nutrients essential to all plant life and they are split into two groups called Macronutrients and Micronutrients. There are 6 Macronutrients and 11 Micronutrients. Macronutrients are the ones needed in larger quantities. Plants need more nitrogen, phosphorus and potassium than any other plant nutrients. These three are called the primary macronutrients and are listed on your bag of fertiliser.
Why the different NPK ratios?
Plants have different needs and your fertiliser has been blended to reflect what they use the most, and require to thrive.
Do you need Fertiliser?
Plants obtain their essential nutrients naturally from air and soil or the mix they are planted in. Over time, soil and mixes get depleted and because plants use larger amounts of N-P-K, these nutrients need frequent replenishing. Not only do the plants use the nutrients, rain and watering may leach these away over time. Fertiliser replenishes used and lost nutrients so that lawns and gardens stay nourished.
The law of minimum and why you need to fertilise.
The law of minimum states that the yield achievable by a plant is dictated by the nutrient that is most limiting. This simply means that if you are short of a nutrient then it will hold back development, even if you have an abundance of other nutrients. As in the picture, the barrel will never fill past the lowest plank unless you raise it. A well-balanced fertilizer will lift the performance of your plant.