Understanding Fertilizer

Fertilizer is simply an alternate source of all the basic nutrients, such as nitrogen, phosphorous, potassium, and trace minerals that exist naturally in a healthy soil. The nutrients in fertilizer products are derived from a wide variety of natural sources such as manures, leaves, bloodmeal, bonemeal, feathers, and other organic materials or they are synthesized in a laboratory from urea and other compounds. Either way, fertilizer feeds the soil, not the plants. It breaks down in the soil, either by being dissolved in water or by microbial action, releasing its nutrients in a form that plant roots can absorb. Plants use nitrogen for leaf production, phosphorus for root and flower production and potassium for flower production and general vigor. Fertilizer products are useful to either compensate for thin, poor soil or to supplement the nutrients existing in healthy soil.

About NKP Numbers

There is considerable variety among fertilizer products, especially lawn fertilizers, in terms of their relative percentages of nitrogen (N), phosphorous (P), and potassium (K), the primary nutrients for plants. The percentages are expressed as a ratio and are prominently displayed as three numbers on the packaging of most brands. If you see the numbers 5-10-5, that would mean that 5% of the product is nitrogen (N), 10% is phosphorus (P), and 5% is potassium (K).
The NPK ratio of a particular product is one way to judge whether it is suitable for actively growing spring lawns which need more nitrogen (N) to actively grow foliage relative to the other nutrients or proportionately more phosphorus (P) for lawns going into winter and are developing root systems. It is not necessary to consider the subtleties of the NPK ratio on a product for routine lawn and garden use. Look for a product that is labeled “all-purpose” or “general purpose” for this situation.

General Purpose vs. Special Purpose

General purpose fertilizers are typically balanced. They contain all three major nutrients which are present in the proportions likely to be found in a healthy soil. These general purpose fertilizers are suitable for use on lawns, trees, shrubs, flowers, even vegetable gardens where there are no special problems with the soil. They are most commonly and easily used in a granular form that can be spread uniformly with a mechanical spreader and watered in by rain or your sprinkler.
Special purpose fertilizers are typically “unbalanced”, featuring a greater proportion of one or the other major nutrients or special trace minerals or enzymes that suit them for particular situations or plants. For instance, there are fertilizers labeled for acid-loving plants such as azaleas and holly that help provide iron in a form that these plants can use. There are bulb fertilizers that provide generous amounts of phosphorus that bulbs require. Some are labeled specifically for lawns, tomatoes or trees. As you learn more about the plants and soil in your yard these special purpose products may be useful. However, a general purpose fertilizer is adequate in most situations.
Here is a very brief listing of what distinguishes the special categories of fertilizer for home use:
· General Purpose Fertilizer - designed to provide basic nutrients for any plant, best for trees and shrubs.
· Lawn Fertilizer - Tends to have more nitrogen which turfgrass needs
· Flower Garden Fertilizer - Tends to have a bit more phosphorous which is needed to help encourage blossoms.
· Vegetable Garden Fertilizer - Higher percentage of all major nutrients since closely planted vegetables need more food.

Synthetic vs. Natural

The nutrients of most fertilizers on the market today are synthesized rather than derived from natural plant or animal matter. They are packaged as liquids or powders to dissolve in water, or as granular products. While many are quick-acting because they dissolve in water, manufacturers have developed technology to coat nitrogen so that it is water insoluble and is released slowly into the soil environment similar to the way nitrogen from natural or organic sources is. These granular, slow-acting synthetic fertilizers are the best type for most situations. Their nutrient particles are uniform in size to promote more accurate formulation and more even distribution when spread on the soil. Chemically the nutrients are exactly the same as those in naturally derived fertilizer products.
Natural fertilizers come the closest to replicating the natural nutrient processes of the soil itself. They are always “granular” or solid, rather than liquid. They are by their nature slow-acting, because they depend on microbial action in the soil to release their nutrients for the plant roots. While each type of fertilizer has its adherents, the critical issue is less that it is organic or synthetic, than whether it is slow-acting. This feature protects the soil and its life and serves the plants better.