How NPK Affects Plant Health

Earlier we gave you a look into what NPK is in our post: “What is NPK?” Now that you know that NPK stands for nitrogen, phosphorus, and potassium, it’s time to learn why these three macro-nutrients are so important to plant health.


Nitrogen is one of the most important nutrients to ensure healthy plant growth as it strongly affects leaf development.

If your plants look yellowish or pale it is probably a sign that they do not have enough nitrogen. If this is your case, you could add some fish emulsion, compost, blood meal, or other nitrogen additive. You should also plan to add some nitrogen fixing plants such as beans, clovers, or peas to your ecosystem.

If your plants look suspiciously dark green and you notice excessive quick growth, it may be a sign that your soil or other grow media has too much nitrogen. Either flush with water or let the nitrogen be naturally used up by plants.

Ideal levels of nitrogen really depends on the plant but can range from 5 parts-per-million (ppm) to 30 ppm. Some quick internet research will tell you the optimum nitrogen level for the plant you are trying to grow.



Phosphorus encourages strong roots, shoots, and stem development. Phosphorus deficiencies can be noticed by slow growth and a lack of flowers or fruit. Too much phosphorus will clog up poor spaces and block other required nutrients to be absorbed by the plants.

Add phosphorus to your soil by adding either bone meal or rock phosphate.

The optimum level of phosphorus also ranges. A measurement of 10-20 ppm is considered a good level of phosphorus for gardening. Again, it depends on the plant and the type of grow media used.


Potassium affects a multitude of growth factors in plants. Potassium promotes: plant growth, resistance to disease, production, thickness, and the efficiency of water use. Potassium is also one of the trickiest deficiencies to spot because it promotes many different growth factors.  Look for yellow or brown veins or spots on the leaves of older plants. Performing a soil test is the best way to find out your potassium levels in your grow media. Add more potassium by using greensand, wood ash, or granite dust.

Ideal levels of potassium are 40 ppm – 130 ppm.

Understanding these macro-nutrients is critical to growing a foison of fruits and vegetables.  There are a lot more nutrients that are important to plant growth.  Get ready for the next article about soil micro-nutrients!



Photos: Kevin Dooley,

PrintBy Jake Frazier

Jake Frazier is an outdoor enthusiast and the owner of Residential Ecology, a sustainable ecological resource management company. He uses existing natural systems to improve the quality of life for both humans and the Earth. Jake is interested in permaculture, living systems and exploring. Connect with him on LinkedIn.

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