Home Vegetable Garden Guide

Fertilizing your Vegetable Plants

While nature can provide most nutrients to a limited degree, it takes years, or even decades for organisms in the soil to build up enough nutrients for a decent crop yield. One crop in virgin soil can mine many years' worth of naturally produced nutrients in a single growing season. When soils have been drained of all the nurtients needed, nature needs a little help.

That's where fertilizers step in.
To make plants grow strong, healthy and fast, what you need to do is supply the 16 elements that the plants need in readily available, water-soluble forms. That is the goal of fertilizer.

When left to fend for themselves, plants can become susceptible to disease and pest they would naturally be able to defend against. Using fertilizer, in combination with organic matter, can greatly improve your garden's success, health and yield.

Plant Nutrient Requirements

In order for a plant to grow and thrive, it needs a number of different elements. There are 16 different elements or nutrients have been found to be essential for crops. These nutrients or elements include three organic, three primary, and three secondary

Carbon, hydrogen and oxygen
The three organic nutrients are taken directly from the air and water.

Nitrogen, phosphorus, potassium (a.k.a. potash)
The three primary macronutrients and the three elements you find in most packaged fertilizers.

Sulfur, calcium, and magnesium
Secondary nutrients

Boron, cobalt, copper, iron, manganese, molybdenum and zinc


The most important of these are nitrogen, phosphorus and potassium. These nutrients are necessary for these basic building blocks of the plants cell structure.

Every amino acid contains nitrogen.

Every molecule making up every cell's membrane contains phosphorous (the membrane molecules are called phospholipids), and so does every molecule of ATP (the main energy source of all cells).

Potassium makes up 1 percent to 2 percent of the weight of any plant and, as an ion in cells, is essential to metabolism.


Without nitrogen, phosphorus and potassium, the plant simply cannot grow because it cannot make the pieces it needs.

If any of the macronutrients are missing or hard to obtain from the soil, this will limit the growth rate for the plant. In nature, the nitrogen, phosphorous and potassium often come from the decay of plants that have died. In the case of nitrogen, the recycling of nitrogen from dead to living plants is often the only source of nitrogen in the soil.


Nitrogen, phosphorus and potassium availability is the big limit to growth and most fertilizers supply Macronutrients. A good fertilizer will also supply the Micronutrients to replenish the soil as well.

"Micronutrients are to agriculture as vitamins are to the human diet." - Braun

Micronutrients are all essential for maximum crop growth, health and yield. Micronutrients are nutrients needed in relatively low quantities by the plant, although micronutrients are often needed in quantities greater than the soil can supply. A micronutrient deficiency in these area can adversely affect plant growth and development.

So what's in your fertilizer?

The numbers on a bag of fertilizer tell you the percentages of available nitrogen, phosphorus and potassium found in the bag or bottle. So 5-4-6 fertilizer is made up of 5% nitrogen, 4% phosphorous and 6% potassium.