A garden requires a proper balance of nutrients to maintain healthy plant growth. When the use of nutrients is greater than the replacement of them, soil degradation occurs, causing diseased and sick plants. Fertilizing the garden replaces these nutrients.
Testing your garden soil before application of fertilizer ensures that the nutrients being put into the lawn will not cause damage to the plants. PH tests are available from most garden centers, with instructions on how to test the soil properly. Soil sampling labs are located at most university extension offices, and are available for a small fee. These services will provide suggestions on how to fertilize your garden properly.
Soil pH is the relative acidity or alkalinity of your garden soil. A reading of 7.0 is a neutral soil, while readings below 7.0 are acidic, and above 7.0 are alkaline, says Montana State University. When acidic, lime is added with fertilizer to balance the soil, while sulfur and fertilizer are added when the soil is alkaline.
Application of fertilizer is recommended according to the plant you are growing, in square feet, says New Mexico State University. Fertilizers are applied according to nutrient weight per 1,000 square feet; for example, cabbage requires 5 pounds of nitrogen per 1,000 square feet, while melons require 1.8. Fertilizer is spread over an area and either buried in the dirt or lightly watered to sink it into the soil.
Nutrient content of a fertilizer is expressed on the bag according to nutrient percentage in the weight of the fertilizer. A 10-10-10 is 10 percent each of nitrogen, phosphorous and potassium by weight. A 24-pound bag of fertilizer would have 5.76 pounds of nitrogen in a bag (24 x .10 = 5.76 pounds), and the same for phosphorous and potassium.
Pollution of lakes and streams from fertilizer can cause the destruction of wildlife and the growth of invasive algae. It is important to protect the garden from fertilizer runoff. Applying light water onto fertilizer to sink it into the soil after application will prevent some runoff, while placing mulch on top of the garden will prevent rain run off, says the University of Missouri. Applying only what fertilizer is necessary will prevent further contamination.