Nearly 70 percent of water pollution comes from agricultural areas that use chemical fertilizers, according to the EPA. These chemicals leach into the water and cause soil erosion. While large-scale farming operations are a chief source of chemical fertilizers in water, home gardeners are also guilty of such pollution. However, many growers are attempting to correct their mistakes by using organic growing methods.

Organic fertilizers are those that use organic soil amendments to raise the nutrient content and improve the soil characteristics of a garden. The addition of decomposing organic materials in an organic garden provides a natural fertilizer, supplying plants with the nutrients they need for optimal growth. These fertilizers also improve the nature of your garden soil, not matter what type you have.

If your garden has clay soil, organic fertilizers preserve its tilth, which prevents it from clumping together. Organic fertilizers are also an excellent means of holding water in the soil. This is a boon if you have sandy soil in your garden. Fertilizers made of organic materials have properties that make micro-nutrients like iron and zinc available to your garden plants.

Plants need three important nutrients in order to grow: nitrogen, potassium, and phosphorous. All three of these are found in organic fertilizers. One organic material - manure, for example, does not have all three of these nutrients, however. Therefore, most organic fertilizer suppliers combine and mix different materials to ensure an appropriate mix.

Alfalfa meal is a green manure favored by gardeners who grow roses. It is a good source of nitrogen, phosphorous, and potassium, and it also contains Triacontanol. This is a hormone that helps to regulate the growth of your plants. Blood meal is another good organic fertilizer. It is an excellent source of readily available organic nitrogen.

Bone meal is a good source of calcium and long-lasting phosphorous. These two materials can be blended together for better results. Kelp meal has a high potassium content, but it has no phosphorous. This organic fertilizer must be used together with bone meal to make up for its lack of phosphorous.

It is important the gardeners check the exact composition of any organic fertilizer they buy, since they can contain a number of micro-nutrients and lack others.