Complete Fertilizer: How To Choose The Right Fertilizer

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Summary: A complete fertilizer or plant food – organic or inorganic – is one very key “item” for success in the lawn, with landscape plants, in your garden, and with your houseplants. With a little study of fertilizers and their recommended uses, you can save money and increase productivity.

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Question: The garden center recommended a “complete fertilizer” to use on the lawn, landscape trees and shrubs for my yard, how do I go about choosing the right fertilizer for my use? Martin, Peachtree, Georgia

Answer: Martin, homeowners face many options in choosing from a great variety of foods for their fertilizer applications on the market today, and may at times be uncertain which one to select for their particular needs.

It’s always best to get a soil test before applying and type of “plant food” the lawn, or garden.

There are organic and inorganic fertilizers, both of which are available in powdered, liquid and granular fertilizer forms.

Then, some are balanced or complete fertilizers; others are prepared for special purposes like a starter fertilizer.

A study of fertilizers and their recommended uses is well worthwhile, both in terms of money saved and in increased productivity.

What Are The Essential Elements of Complete Fertilizer?

A complete fertilizer must contain three basic elements of plant nutrients:

  • (1) Nitrogen, which promotes leaf and stem growth
  • (2) Phosphorus, which helps plants grow and flower as well as makes their stems strong
  • (3) Potash, (potassium) which aids root growth and, to a certain extent, acts as a balance wheel between the other two.

By law, the percentage of these three fertilizer elements making up the “plant food” must be printed on the bag or container.


The percentage, or the number of pounds of each fertilizer element per 100 pounds, is expressed in numbers such as:

  • 10-5-5
  • 5-10-10
  •  5-8-7
  • 20-20-20

… and so forth, and always in the same order: nitrogen, phosphorus, and potassium also known as n-p-k ratio.

For example, a low nitrogen fertilizer 5-10-10 is such because the 1st number represents nitrogen content.

If the total amount of each element in a particular fertilizer is not in a form which plants can use as plant food, the analysis must also show the percentage which is available to plants.

Many fertilizers also contain some:

  • Iron
  • Copper
  • Manganese
  • Calcium

… etc., which may or may not be listed. The bag also lists the recommended amount of fertilizer material to apply per square foot.

What Are The Basic Types Of Plant Food Fertilizer?

There are several ways to classify fertilizers, but first we shall divide them according to whether they are organic or inorganic.

Complete organic fertilizers are those derived from animals or from plants.

Bone meal comes from ground bones of animals and other waste materials from the slaughterhouse.

Widely used as an organic fertilizer due to its high phosphorus and protein content.

Blood meal or dried blood serves as one of the highest nitrogen sources. It also provides high protein content.

This comes as a dry, inert powder made up of cattle or pigs blood from the abattoir.

Fish emulsion fertilizer or fishmeal,  this organic fertilizer develops from bones, left-over offals, and wild-caught, small marine fish.

This fertilizer delivers more protein than any other plant nutrients.

According to EPA in the US, treated and recycled sewage sludges (milorganite) for sustaining and improving productive soils. Also, it distributes enough plant nutrients that support plant growth. [source]

Cottonseed meal comes as a by-product of cotton and works as a slow-release fertilizer which everyone sees as a high-quality nutrient recommended for great plant growth.

This slow-release fertilizer improves soil texture, aids in the production of humus, and protects the soil from rapid erosion.

On the other hand, kelp meal or seaweed fertilizer serves as another good organic amendment to the soil. It wakes up microbes in the soil to help break down organic matter for plants to consume.

Manure (fresh or dried), derived from animal feces is a common organic fertilizer used by farmers to cultivate the soil.

High in organic matter and nutrients, this material greatly contributes to the fertility of the soil and a bounty harvest. You find manure often mixed with compost.

These materials are comparatively low in their chemical analysis but they often appear to furnish benefits out of proportion to their content.

They cannot burn your plants and they release their chemicals slowly as they gradually decay.

Natural Chemicals In Fertilizer

The inorganic fertilizers are already in their basic chemical form. A number of them, like some limes and rock phosphates, are natural chemicals.

Others are manufactured chemicals. Since they are already in chemical form – which is the only way in which the plants can absorb them regardless of their origin – they take effect much faster than organic fertilizers. Decay is not necessary.

Other points in their favor are that they are usually cheaper, you can control more accurately the amount of plant foods you provide.

They also have higher concentrations of plant fertilizers so that you need less inorganic than organic fertilizer to do the same job.

What Is Synthetic Fertilizer? = Man-Made Chemicals


To confuse us, however, science has now given us synthetic organics, man-made “natural foods.”

These fertilizers are members of the urea-form group, relatives of the plastics, and release their one plant food, nitrogen, slowly as they decay.

In the North they may release it over the entire growing season; in the South they break down more quickly.

Although they are highly concentrated – containing up to 40 percent, or more – they cannot burn roots or leaves. Nitroform has been a widely advertised brand.

Liquid Fertilizers

A third basic group is the water-soluble liquid plant fertilizers.

Here we include both types the organic liquid fertilizers such as the liquid fish emulsions and the purely chemical, or inorganic, water-soluble fertilizer powders and liquids.

Both are convenient to use and equally effective in the soil. The inorganic group, however, lends itself to somewhat more rapid absorption when used for foliar or on-the-leaf feeding.

They usually come in more highly concentrated form and a little goes a long way. But, by the same token, they must be used with greater care and strict adherence to the manufacturer’s instructions.

Specialized Fertilizer

Finally, we have a specialized complete fertilizer such as lime-free Azalea bush food, Camellia, and holly fertilizers, natural rose fertilizers, bulb foods, and African-violet fertilizers etc.

Their uses are indicated by their names. In this category, too, are the common gypsum, used in limestone sections to supply calcium without increasing alkalinity, and sulfur, used as a minor plant food and soil acidifier.

Fertilizer By Content Type

We can also divide fertilizers into two groups according to their contents.

One is the high-nitrogen fertilizer type, which promotes leafy growth on lawns, leaf vegetables, and foliage plants – this is why you should Know the Fertilizer numbers.

A good example of this is 10-5-5, used as a grass fertilizer in some areas. The other is the low-nitrogen type, in which phosphorus and potash play a more important part.

One of these is 5-10-10, used primarily as a tree, rose, and bulb food. Use the first type where stem and leaf growth is wanted and the second where flowers and fruits are important, as well as for all root crops.

Hopefully, you now have a better idea of the fertilizer you need for the job and can now buy the “complete fertilizer” needed to do the job.

Recommended Reading

Read More On: Applying Fertilizer… How Much

How To Use Plant Fertilizer Concentrates

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