There is a lot of confusion on what truly can be designated an organic fertilizer. An organic fertilizer contains nutrients that have been derived, in one manner or another, from an organism. As an example, organic fertilizers may be manufactured from cottonseed meal, an emulsion derived from fish, animal manure, sewage sludge, and bone meal or a combination of some or all of the aforementioned items.
Some fertilizers that call themselves organic are made from Urea, which is made from inorganic products hence at best it is a synthetic organic fertilizer.
If a product is sold as a fertilizer in North America, it must state the NPK (nitrogen, phosphorus, potassium) formulation on the package. In order to avoid having to guarantee a NPK of a product, many manufacturers will sell their fertilizers as soil conditioners. A soil conditioner does not have to state the nutrient formulation of the product. One of the reasons that manufactures do not want to state a guaranteed nutrient formulation is that with organic products the nutrient levels vary dramatically from batch to batch. Organic products that are made from sewage sludge and manures will only have small amounts of nutrients present in the formulation.
Some organic fertilizers are fortified in order to bring up the nutrient levels and to allow the manufacturer to maintain a guaranteed level of formulation.
Organic fertilizers work best in moist warm soils as it is the organisms in the soil that breakdown the fertilizer which is what releases the nutrients into the soil. Because an organic fertilizer must be broken down in order for it to provide any nutrients to the soil, organic fertilizers are classified as very slow release and a gardener must determine if a slow release is what any specific plant variety might need.
It is also important to understand the side effects of the organic fertilizer. As an example, cottonseed meal is acidic. If you are growing plants such as azaleas or rhododendrons, an organic fertilizer derived from cottonseed meal may be the exact product you are looking for. The common formulation for cottonseed meal is 7-3-2.
With an organic fertilizer such as blood meal, derived from the blood of cattle, one must be cautious because it has a very high nitrogen content and if not used carefully can easily burn plants.
Organic fertilizers have there place in the garden, but they are no different than synthetic fertilizers in the fact that you must understand the formulation of the product and how it might negatively affect the specific plants that you are trying to enhance.
Read and follow the manufacturers instructions and guidelines before usage!
Additional information on orgainic fertilizers.
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