Analysis of Fertilizers

N-P-K Ratio

• Commercial fertilizers typically contain a ratio of nitrogen, phosphorus and potassium, expressed as an N-P-K ratio. The numbers on the fertilizer label represent the percentage of each nutrient that the fertilizer contains; for instance, a 20-20-20 fertilizer possesses 20 percent nitrogen, 20 percent phosphorus and 20 percent potassium. If a fertilizer doesn't contain one of these main nutrients, the label places a zero instead of a number to represent its absence. An example is a nitrogen fertilizer that may have a 20-0-0 label, indicating 20 percent nitrogen with no phosphorus or potassium.

What the Nutrients Do

• Each of the three main nutrients has a specific purpose. Nitrogen is responsible for green growth, which makes it a must for leafy plants such as grass and lettuce. Phosphorus aids the growth of roots and flowers, while potassium is necessary for plant metabolism and stress tolerance. Bloom booster formulas contain extra phosphorus to induce flowering. Some fertilizers also contain macronutrients, such as iron, calcium and magnesium.

Complete vs. Incomplete Fertilizers

• Complete fertilizers contain all three of the main nutrients, while incomplete fertilizers are missing at least one of them. Some plants prefer incomplete fertilizers. For instance, grass benefits from nitrogen fertilizer, which supports green growth. You can also perform a soil test with a home soil test kit to pinpoint nutrient deficiencies in your garden, if any exist, and treat the deficient areas with an incomplete fertilizer containing the deficient nutrient.

Release of Nutrients

• Fertilizers come in two main types: quick-release and slow-release. Quick-release fertilizers act fast in the garden, flooding the soil with nutrients to promote rapid growth and remedy nutrient deficiencies. Meanwhile, slow-release fertilizers gradually flush nutrients into the soil over the course of several weeks, which can keep a garden well-fed for longer and prevent root burn from too much fertilizer, too fast. Similarly, synthetic fertilizers that contain chemicals usually decompose rapidly into the landscape, while organic fertilizers -- such as fish emulsion, cottonseed meal and blood meal -- release nutrients gradually.