Organic vs inorganic fertilizers

Healthy soil has a variety of nutrients in it to help your plants grow strong enough to defend themselves from most (but not all!) pests and diseases. Soilless mixes, like you'd use in a pot or a container, do not contain any soil at all. They are typically a mix of peat moss, perlite, and vermiculite and have almost zero nutrient value. They are essentially organic sponges. Unless you add fertilizer, in the form of compost or other types of fertilizer, your plants will not produce well and will be prone to many pests and disease issues.

What is a fertilizer?

By definition, a fertilizer is "any organic or inorganic material of natural or synthetic origin which is added to a soil to supply elements essential to the growth of plants." (Brady, Soils, 1974)

What exactly does that mean? Organic means something which is or was alive. Animal manures were once living plants. Bonemeal, a by-product of slaughter houses, is composed of ground- up bones of animals. Inorganic means from non-living sources. Rock phosphate, a common source of phosphorus, comes from rocks, a non-living material. The term natural describes the manure, the bonemeal, and the rock phosphate. All are naturally occurring. The term synthetic describes such products as nitrogen fertilizer manufactured by combining natural gas with nitrogen from the air.

Organic vs. Inorganic

There has been much controversy over organic versus inorganic fertilizers. It is important to realize that plants do not recognize the difference between organic and inorganic fertilizers.  As long as these elements are supplied in adequate amounts it makes little difference to the plant if they are organic, inorganic, natural or synthetic. Their tiny root hairs can absorb only nutrients that have been broken down into inorganic, water-soluble forms. It makes no difference to your tomato plant if the atom of nitrogen it is absorbing has come from a compost pile or a fertilizer factory. There are, however, advantages and disadvantages to each form of fertilizer, organic and inorganic.

Organic Fertilizer

Advantages - Organic nutrients include such things as cow, sheep, poultry and horse manure. (One should avoid using pig, dog or cat feces because of the problems involved with internal parasitic worms which may be transferred to humans.) Bonemeal, bloodmeal, compost, and green manures will also provide nutrients for your plants.

There is less danger of over-fertilization by adding decomposed organic material to a garden. It provides a slow release of nutrients as micro-organisms in the soil break the organic material down into an inorganic, water soluble soluble form which the plants can use. The addition of organic material improves soil structure or "workability" immensely. It also vastly improves the water-holding capacities of sandy soils, a distinct advantage in arid climates such as ours.

Disadvantages - For the most part, organic fertilizer is not immediately available to the plants. As noted above, this "slow- release" feature can be an advantage. However, if there is an immediate need for nutrients, organic fertilizer cannot supply them in a hurry. Furthermore, information on the amount of nutrients and the exact elements in an organic fertilizer such as manure is not readily available to the home gardener. In contrast, when you apply manufactured inorganic ferilizer you know the kinds and amounts of the elements it contains, and this allows you to be more precise in meeting a plant's nutritional needs.

The possibility of nitrogen depletion is another drawback of organic fertilizers. Because of complex bacterial action, the addition of a large amount of organic material can cause a temporary nitrogen depletion in the soil and therefore in the plants.

Inorganic Commercial Fertilizer

Advantages - The primary advantage of using packaged commercial fertilizer is that nutrients are immediately available to the plants. As well, the exact amounts of a given element can be calculated and given to plants.

Disadvantages - Commercial fertilizer, especially nitrogen, is easily washed below the level of the plant's root system through the leaching of rain or irrigation. An application which is too heavy or too close to the roots of the plants may cause "burning" (actually a process of desiccation by the chemical salts in the fertilizer). As well, overly heavy applications of commercial fertilizers can build up toxic concentrations of salts in the soil, thus creating chemical imbalances. If organic materials are readily available and cheap, the expense of the commercial fertilizer should also be considered.

Whether a gardener chooses to use organic, inorganic or a combination of both types of fertilizers, it's important to follow the guidelines regarding timing of application, placement of the fertilizer, and the proper amount of fertilizer to be used.