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Understanding Fertilizers

© Kenneth Joergensen

Fertilizing is very important, especially to young plants which must put on lots of growth. Unfortunately, the process is very often misunderstood. In this segment we will explore why fertilizing is required and how.

Why fertilize
Plants, like humans, need some basic nutrients to grow and prosper. If key nutrients are missing growth will be limited or in worst case death will follow. Typically, the plants will get what they need from water (rain), air (atmosphere), and from the soil. If one or more nutrients are lacking in the soil, we must manually re-supply these nutrients.

The key nutrients which are required by the plants are usually divided into 4 main groups:

1) Carbon, Hydrogen, Oxygen (supplied from the air, specifically carbondioxide, and water). These are the 3 molecules used to create carbohydrates, e.g. the energy source from which the plant growth.

2) Nitrogen, Phosphorous and Potassium (also called NPK nutrients). These primary macro nutrients must be supplied on a regular basis as manual fertilization. They are typically the key objective when fertilizing.

3) Calcium, Magnesium, and Sulfur, are also called the secondary macro nutrients. They are usually supplied in adequate quantities by actions such as liming and through the water, or in combination with the 3 primary macro nutrients. Typically no further action is required by the grower. E.g. by using "sulfate of potash" to supply potassium, sulfur is automatically supplied. Liming the growing medium with dolomitic limestone, the pH is adjusted and magnesium and calcium are automatically supplied.

4) The micro nutrients: Iron, Chloride, Manganese, Molybdenum, Copper, Boron, Zinc, and Nickel. These are needed in much smaller quantities and outdoors in soil additional fertilization is seldom required. Indoors, in soil-less growing media, however, even these nutrients may need to be added, and the easiest way would be to use a complete fertilizer which includes micro nutrients.

Fertilizing is thus simply the process of re-supplying nutrients to the plants which has been used up in the soil. Some nutrients, carbon for example, are not added manually as it is extracted by the plants from carbon dioxide. Other nutrients, like Nitrogen, must be re-supplied manually, and often, as the plants consume large quantities of this element; typically more than nature can re-supply on its own.

Plant Food?
A very common misunderstanding - which is aggravated by the fertilizer industry itself through advertising - is to call fertilizer "Plant Food". Plants do not eat fertilizer. Instead fertilizer can be considered "supplements" akin to our vitamins or raw materials: raw materials for food or even raw materials for the "factories" which are build and which the plants utilize to produce their own foodstuffs. This unique ability is called "photosynthesis" which is the conversion of essential nutrients into carbohydrate using the sun's energy as energy source (now you know why plants require sunshine).

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