With good crop rotation, some gardeners with exceptionally good soil may not need fertilizers for a vegetable garden. However, most people have soil that is far from perfect, and many people are not in a position to rotate crops for ideal nutrient cycling. Therefore, most vegetable gardens benefit from proper fertilization. Because different crops have different fertilizer requirements, using a balanced fertilizer is best. A balanced fertilizer has equal percentages of the three major plant nutrients.
Major Required Nutrients
Vegetables require three main nutrients to grow. One is nitrogen, the second is phosphorus and the third is potassium. These nutrients are listed on all chemical fertilizers and some organic fertilizers as N-P-K values. N-P-K values are the percentage of by weight of these nutrients. For example, 10-10-10 fertilizer has 10 percent of each nutrient by weight, meaning that a 10-pound bag of fertilizer would contain one pound each of nitrogen, phosphorous, and potassium.
Chemical vs. Organic
There are two sources of these three main vegetable nutrients. The oldest forms are organic fertilizers, or fertilizers derived from natural sources. The second, and more modern, are chemical fertilizers. Organic fertilizers are gentler. The base nutrients in organics require some breakdown before they will be ready for the plants to use. This process encourages soil health, including encouraging beneficial microbes. Chemical fertilizers, on the other hand, are in the form that the plants require, and can be quickly absorbed by the plants. However, it is easier to over-fertilize with chemical fertilizers. Over-fertilization can damage soils, cause runoff that creates problems in waterways, and can sometimes cause damage to the plants and roots.
Lawns need fertilizers that are high in nitrogen. Nitrogen triggers green leafy growth more than the other fertilizer components. The most common source of nitrogen in chemical based lawn fertilizers is ammonium nitrate. Sources of nitrogen in organic fertilizers include bat guano, animal and poultry manures, and composted plant material. Seed meals are also a source of nitrogen in organic lawn care and organic lawn fertilizers. Blood meal, feather meal, fishmeal, and crab meal are also sources of nitrogen that you can used in organic grass fertilizer blends.
Ground rock phosphate can be a source of phosphorous in grass fertilizers. However, because of a low supply and high transportation costs, very little rock phosphate is used in commercial fertilizer production. Most commercial chemical fertilizers use phosphoric acid, which breaks down in the soil into usable phosphorous. There are fewer sources of phosphorus in organic lawn fertilizers than for nitrogen. One source of phosphorous for organic lawn care is bat guano. Bone meal is another good source of organic phosphorus. Rock phosphate is also used in organics, as a natural source of phosphorus.
Potassium in chemical lawn fertilizers can come from a variety of sources. Potassium chloride is a common chemical source, as are potassium sulfate, potassium nitrate, and a combination of sulfur, potassium and magnesium called So-Po-Mag. Natural rock sources of potassium are sometimes used in organic fertilizers, as is cottonseed hull ash, grape skin ash, and a number of different animal and poultry manures.