Organic gardening and agriculture focus on the improvement of soils to provide plants with nutrients. Conventional fertilizers, on the other hand, often deplete soils of beneficial microbes and organic matter (see References 2). Organic fertilizers come from organic plant or animal sources and contain at least 5 percent of nitrogen, phosphorus or potassium combined -- the primary nutrients plants need. Organic fertilizers may also contain mineral supplements, such as calcium or magnesium. (See References 1)
Collect a soil sample and submit it for nutrient testing. Before you apply any fertilizers, you should know what your soil needs, as well as information about optimal or excessive nutrient levels. University extension offices and private testing companies can perform low-cost soil tests and will provide precise instructions on how to prepare and send in a sample for testing.
Interpret soil test results. Most testing labs will indicate nutrient levels on a scale ranging from very low to very high, allowing you to identify nutrients you need to provide as part of your fertilizer regimen. The test will also provide a fertilizer recommendation, expressed as three numbers, such as 10-5-5. The numbers indicate the proportion of nitrogen, phosphorus and potassium you need in your fertilizer. (See References 3)
Purchase an organic fertilizer that closely matches the fertilizer number recommended on your soil test. You will find the fertilizer numbers prominently displayed on the front of the fertilizer packaging.
Spread the recommended amount of dry fertilizer over the garden area. With a garden fork or rake, work the fertilizer into the top 4 to 6 inches of soil.
Never exceed the application rates recommended on your soil test or, if you're working without a soil test, the fertilizer packaging. Fertilizers, particularly those heavy in nitrogen and phosphorus, are major pollutants of surface and ground waters worldwide (see References 5). Although the blame tends to be placed on users of conventional fertilizers, a 2007 study published in "Environmental Pollution" found that organic fertilizers have the potential to act as pollutants as well (see References 6).
Add a handful of organic fertilizer to the planting hole as you plant seeds or transplant seedlings. Unlike conventional fertilizers, all organics are slow-release, so you don't have to worry about a sudden overabundance of nutrients burning your plants' roots (See References 4, p. 229).
Work dry organic fertilizers into the top inch of soil around existing plants.
Dilute and mix foliar liquid fertilizers according to the instructions on the packaging. Use a hand sprayer or backpack sprayer to apply these fertilizers directly to foliage to give plants extra nutrients during the growing season. (See References 4, p. 230)
- United Nations Food and Agriculture Organization; Introduction; March 2007
- Virginia Association for Biological Farming: How to Use a Soil Test: Mark Schonbeck
- "Rodale's Ultimate Encyclopedia of Organic Gardening"; Fern Marshall Bradley, Barbara W. Ellis and Ellen Phillips, editors; 2009
- Food and Agriculture Organization of the United Nations: Fertilizers as Water Pollutants
- "Environmental Pollution"; Ecological Risk Assessment of Organic Waste Amendments ...; Xavier Domene, et al.; 2008