NPK: the three magic letters of the garden.But what do they really mean?
The three nutritional bigwigs of the plant kingdom are nitrogen, phosphorous and potassium. These nutrients are essential for plant growth and deficiencies can play havoc in your garden.
“N” is the kingpin of the trio. It stands for nitrogen and without it there would be no plant life – or any other life, by extension. In addition to being part of all proteins in animal and plant life, nitrogen is a critical component of DNA and RNA.
If you notice the leaves on your plants fading to a yellowish green (without showing the veins), it could be symptomatic of a lack of nitrogen. A nitrogen deficiency can slow down chlorophyll production. Nitrogen also helps plants to utilize the water from rainfall and soil moisture.
Nitrogen used by plants comes from organic matter, not from minerals. As nitrogen in organic matter is being broken down by the action of bacteria and other microbes, it is converted to a simpler form, ammonium and nitrate, both soluble in water and accessible to plants. The ammonium form is captured by soil particles and does not get washed away by the flushing action of water during rainfall or irrigation.
In addition to getting nitrogen from decaying organics and the chemicals you may add to the garden, plant-accessible nitrogen is available from electrical storms, which release vast amounts of nitrogen into the earth.
Nitrogen in the form of ammonium can also be released by leguminous plants, which can “fix” nitrogen in the soil in nodules attached to roots, making it available to other plants.
The “P” in NPK stands for phosphate. It too exists in every living cell and is considered the energizer in fertilizer. Phosphorous helps build genes and chromosomes and is involved in creating the patterns for seed germination and in passing on generational information.
Plants that appear sickly or weak are often phosphorous deficient, because root uptake of nutrients is dependent in part on phosphorous. Even the fixation of nitrogen by leguminous plants requires the action of phosphorus to make this happen.
Phosphorous is available in organic soil particles and can be released through the action of bacteria and microbes as organic materials decay, and from phosphate rock.
Phosphorous does not leach from the soil as nitrogen can but rather remains available for many years. Phosphorous in the form of fertilizer reacts quickly with the soil, becoming available to plants almost immediately when it is applied.
Phosphorous is most beneficial to plants during early growth stages to help get roots established.
The final letter, “K” is really a “P” or potassium, often referred to in fertilizer terms as “potash”. “K” is potassium’s chemical symbol. It is the third most abundant mineral in our bodies, exceeded only by calcium and phosphorous, and it is found in every cell. Potassium is essential to human life and will often be added to the medical regimen of heart and blood pressure patients to counteract other medication side effects. Athletes add supplemental potassium to their diets to maintain levels lost with fluids.
In plants, potassium deficiency may not be evident until it is too late. Strawberries may not sweeten, corn stalks may break or tomatoes may not fully develop.
Potassium helps to improve plant resistance to disease, water stress and pests. It help plants get through winter, keeps sugars moving out of leaves, and works to help form plant protein and starch. It is used by the plant in the process of opening and closing leaf pores (called stomata) and assists with photosynthesis.
Potassium reduces wilting by building cellulose, water loss and it helps root growth.
The impact of chemical fertilizers
There are both upsides and downsides to the use of any additives to the soil, whether it be chemical or organic. While organic fertilizers promote healthy soil, they take time to work. As well, improperly prepared organic fertilizers may contain pathogens that can be harmful to plants or even humans. Careful composting should resolve this issue.
Chemical fertilizers, on the other hand, can add an immediate boost to a plant or a crop that needs it, but overuse can lead to buildup, especially in potted plants. Use only when the sun is shining or when there is sufficient daylight.
Perhaps the best rule of thumb is to always add organics to your garden if you can and use the chemicals like candy, to treat or boost a plant in need.