Organic fertilizer is any fertilizer that is natural, and does not include any man-made chemicals. It comes from the Earth and does not harm the planet. The use of organic, rather than chemical, fertilizers is preferred by many gardeners.
There are several kinds of organic fertilizers that occur naturally. Manure is a commonly used organic type of fertilizer, and consists primarily of animal dung. Worm castings is a type of fertilizer created by earthworms digesting, and excreting organic materials. Seaweed, and bat guano are also used for fertilization. There are also types of organic fertilizer that are processed from naturally occurring materials. Compost is one such type, and consists of biodegradable materials that have been allowed to break down, and partly -- if not mostly -- decay. Fish emulsion is made by blending decomposing fish, and it has very high nitrogen levels. Bone meal is ground bone, and is particularly good for the slow release of nutrients into soil.
Using organic materials to fertilize, rather than chemicals, has benefits. Being organic, it can improve the structure of soil, which helps to prevent soil erosion. The improvement of the soil's structure can help moisture retention. The release of nutrients happens more slowly with organics than it happens with chemical fertilizers, which release all nutrients in one burst after application. Because of the slower release of nutrients, organic fertilizers do not require re-application as frequently as chemical fertilizers. Perhaps most importantly, organic material will not pollute the soil, or underground water sources. Chemical fertilizers can leech harmful products deep into the soil. While chemicals can produce amazing results in the garden, they can also be harmful to the planet over time.
The phrase "going green" can describe the use of organic fertilizers. While they contain no unnatural chemicals, and therefore do not hurt the planet, they are also often made from byproducts. Manure is animal waste. Bone meal, and blood meal are slaughterhouse wastes. Compost can be made from household waste. There are also types of processed seed meals made from seed castings after harvesting, and the extraction of oils have been completed.
Gardening should not be detrimental to the Earth. Using organic fertilizer instead of chemical fertilizer is a good way to reduce our carbon footprint. Organic products re-use waste materials, and can be beneficial to the soil in which it is used in the long term. If that isn't important enough, the prices of organics can sometimes be a fraction of what chemicals can cost.