Although I'm an advocate of compost as a "complete feed" for most lawn and garden settings, some situations require the application of additional natural fertilizers. Earth-wise use of any fertilizer requires more information than the so-many-pounds-per-100-square-feet recommendation on the label. We need to know (1) the existing level of fertility in our soil and (2) the nutritional requirements of the plants we're feeding.
Soil tests are simple to conduct, and lots of how-to Web sites, such as www.soilfoodweb.com, are available for those who need more information. The test results will tell you what is needed to balance your soil's fertility. Then make sure you have a reference book that describes the nutrient requirements of the plants you're growing.
Although most fertilizers are sold as blends such as 2-4-2, which is 2 percent nitrogen (N), 4 percent phosphorus (P), and 2 percent potash, a source of potassium (K), I prefer to formulate my own as a way of making sure each kind of plant receives just what it needs. Some common sources of organic nitrogen are blood meal (fast-release), alfalfa meal (medium-release), and feather meal (slow-release). Nitrogen should always be applied in accordance with the needs of the plant rather than on the basis of the results of a soil test. Most labs don't attempt to test for nitrogen anyway. Phosphorus sources are usually bone meal and rock phosphate. Potash needs can be fulfilled with a combination of sulfate of potash and Jersey Greensand. Greensand and kelp meal are good sources of trace minerals.
The soil test should also indicate whether lime is needed to correct pH balance, an important factor in maintaining good soil health, and should provide readings of calcium (Ca) and magnesium (Mg).
Although natural fertilizers are slower-acting than chemical fertilizers, they are also less likely to leach out of the soil and become problems in the environment.