Basics of Fertilizers

A healthy garden requires attention to the nutrition of the plants. The application of fertilizer is important to the health of the garden. Soil pH affects the availability of nutrients to the plants and is an important consideration when applying fertilizers. Weeds and other nearby plants can rob the soil of fertility. A good soil test reveals the present soil conditions and recommends necessary soil amendments. Micronutrients and other soil amendments are sometimes needed.

Fertilizer Labels

All fertilizer labels contain three numbers, such as 8-16-8. These numbers, sometimes called the N-P-K, indicate that the fertilizer contains 8 percent nitrogen (N), 16 percent phosphorus (P), and 8 percent potassium (K). The remaining bulk of the fertilizer will be inert materials and sometimes micronutrients.


Nitrogen is essential for the development of healthy foliage. Often, nitrogen is depleted from the soil from previous years growth and needs to be added every season. Two forms of nitrogen are available for plant use: ammonium nitrogen and nitrate nitrogen. Ammonium nitrogen converts into nitrate nitrogen over time and lowers the pH of the soil.


Phosphorus promotes good root development. It also promotes flowering and the production of fruit and seeds. Super bloom fertilizer formulas designed to stimulate flowering are high in phosphorus. Phosphorus availability to the plant is affected by soil pH, with best absorption between pH 6.0 and 7.0.


Potassium is also required for healthy plant growth, but its role is not well documented. Potassium in fertilizer is commonly obtained from muriate of potash, 0-0-60. Excess potash can cause a buildup of salts in the soil and damage to the plants.

Organic Fertilizers

Organic fertilizers usually contain nutrients in lower percentages than chemical fertilizers, so more fertilizer may be needed for the same effect. The nutrients in organic fertilizers are in a form that is not readily available to the plants and must be chemically changed in the soil. This process makes the nutrients available over time. Organic fertilizers are usually more expensive to purchase.

Applying Fertilizer

Fertilizers need careful application to avoid damaging the plant. When preparing the garden bed, mix them into the soil before planting. For fertilizing the lawn or trees, spread fertilizer evenly on the surface of the soil and then water the ground. In row or band applications, fill small furrows on either side of the plant. Do a soil test to determine the type and amount of fertilizer needed. A soil test will help you avoid the overuse of fertilizers and lead to healthier plants. Normal application of fertilizer is approximately two or three pounds of fertilizer per 100 feet of garden row. Leafy plants and vegetables require a high nitrogen fertilizer such as 12-12-12 or 15-15-15. Fruiting vegetables and root vegetables need the higher phosphorus concentration found in a 6-12-18 or 6-24-24.

Keywords: basics of fertilizer, how to use fertilizer, fertilizing the garden

About this Author

Diane Watkins has been writing since 1984, with experience in newspaper, newsletter and web content. She writes two electronic newsletters and content around the web. Watkins has a Bachelor of Science degree in chemistry from Clemson University. She has taken graduate courses in biochemistry and education.