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Art Knapp
So Much More Than Plants
Art Knapp

Art Knapp Articles

What do the numbers mean on fertilizers?

in Informational

As you may have seen in your local garden center, fertilizers often have 3 numbers on the front of the packages. "10-10-10", "5-7-3", "12-4-8". Any of these ring a bell? We know that these numbers mean something... but what??

ak fertlizer

Fertilizers consist of three basic elements that are critical to plant health: (N) Nitrogen, (P) Phosphorus, and (K) Potassium. Let's break it down.

Nitrogen = Green growth


Nitrogen (the first number) is necessary for aboveground growth of plants. It is considered one of the most important plant nutrients. Nitrogen is used to make proteins that build cell material and plant tissue, promoting growth of the stems and leaves, which is especially important for leaf crops, such as cabbage, lettuce , and spinach. In addition, it is necessary for the function of other essential biochemical agents. Of all the major plant nutrients, Nitrogen is often the most important deciding factor in plant growth and crop yeild.

Nitrogen deficiency causes stunted or slow growth, slender fibrous stems, and the classic yellowing of leaves, and in severe cases, dropping of the leaves. Younger leaves remain green longer, because they receive soluble forms of nitrogen transported from the older leaves.

Nitrogen deficiency

Picture via migardener.com

Excess nitrogen, however, can also cause problems. Too much Nitrogen can produce excess vegetation in certain crops where excessive leaf development is detrimental, reducing the quality of the root, fruit, or flower.

Phosphorus = Big Blooms, Big Yeilds

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The phosphorus (the middle number) content of a fertilizer is calculated as a percent of the phosphate present. Phosphorus helps plants transport and assimilate nutrients. It is a major building block in all living plants. Phosphorus is responsible for the storage of energy. The energy stored allows for the transportation of nutrients across the cell walls of the plant. Good plant phosphorus levels ensure that crops will reach their full potential for healthy development of fruit, flowers, and a strong root system that ensures better resistance to root rot diseases. 

Phosphorus deficient plants are usually dwarfed and spindly. The leaves, in contrast to those lacking nitrogen, are often dark green with purple tints. The underside of the leaves are usually reddish or purple. Leaf veins and margins often turn bronze. Deficiency symptoms occur first in more mature leaves. Fruit development is usually delayed.


Picture via eplants.com

Potassium = Overall Health

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The potassium (the last number) content of a fertilizer is calculated as percentage of the potash present. Potassium enables plants to develop strong, thick stems, healthy roots, and large, plentiful fruit. Plants require larger quantities of potassium than any other nutrient. Potassium is associated with movement and retention of water, nutrients, and carbohydrates in plant tissue. It stimulates early growth and hastens maturity. Potassium is a key nutrient in a plant's tolerance to stresses (such as cold or hot temeratures), improves resistance to pests and diseases, and is essential for the development of fruits, flowers, and seeds.

As with nitrogen and phosphorus, potassium is easily redistributed from mature leaves to younger ones. Therefore, deficiency symptoms will appear first in the older leaves. These become ash-grey coloured instead of deep green, will look "scorched" at the edges, and start to crinkle or curl with mottled, yellow tips that later turn bronze. Plants deficient in potassium often develop weak stem and stalks, small fruit, and shriveled seeds, along with poor growth and yeilds. They also become more susceptible to disease.

potassium deficiency symptoms in oilseed rape

Picture via pda.org.uk

Together, these three elements form that magic formula, N-P-K; the backbone of all fertilizers, man-made or organic! Think your plant might have a deficiency? Come see us at 4391 King George Blvd., and let our experts help find the right fertilizer for you!

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