Fertilisers are one of the most important tools at the disposal of any successful gardener. Every soil is rich in some nutrients and deprived of others; using a fertiliser can supplement the nutrients that your soil otherwise lacks and increase your chances of successful growth of myriad types of plants. There are two basic types of fertiliser -- organic and chemical (which is synthetic or inorganic). Understanding the differences between each type is essential to knowing which one is right for your gardening needs.
Chemical, synthetic or inorganic fertilisers are distinguished form organic fertilisers by the fact that they derive nutritional content delivered to plants from synthetic compounds rather naturally occurring organic materials like animal manure, fish emulsion, bone meal and bat guano. Since both types of fertiliser promise to deliver the same nutrients to your plants, you may be tempted to conclude that it doesn't matter whether you use organic or inorganic fertilisers; you'd be wrong. There are advantages and disadvantages to using synthetic fertilisers.
Arguably the biggest advantage of chemical fertilisers is that they tend to cost much less than organic fertilisers. The higher cost of organic fertilisers is due not only to the need to harvest organic material to use in the fertilisers but also to the higher costs of being certified organic by government regulatory agencies. The promise of equivalent nutritional content and lower purchasing costs greatly popularised synthetic fertilisers and, according to one scholarly source, "has greatly increased crop yields and made the green industry more cost efficient."
Recent concerns over the environmental effects of using synthetic fertilisers have led many to reconsider synthetic fertilisers as a suitable alternative to organic fertilisers. On the production side, synthetic fertilisers require more fossil fuels to produce and create more greenhouse gases during production than do organic fertilisers. Some of the synthetic compounds used to manufacture chemical fertilisers can have negative environmental effects when allowed to run off into water sources. There is also some evidence that plants treated with chemical fertilisers do not yield as productive results as those treated with organic fertilisers.
In addition to personal choices with regards to cost, environmental concerns and growth choices, there are other considerations to make when trying to choose what fertiliser is right for your garden. Many plants respond better to one type of fertiliser versus another. In other words, organic fertiliser is not categorically more beneficial to plants than is chemical fertiliser, and neither is the reverse true. The choice of which fertiliser to use should be based primarily on the plants you are growing and on your own preferences.